Second Bulgarian Empire

In 1018, when the Byzantine Emperor Basil II (r. 976–1025) conquered the First Bulgarian Empire, he ruled it cautiously. The existing tax system, laws, and the power of low-ranking nobility remained unchanged until his death in 1025. The autocephalous Bulgarian Patriarchate was subordinated to the Ecumenical Patriarch in Constantinople and downgraded to an archbishopric centred in Ohrid, while retaining its autonomy and dioceses. Basil appointed the Bulgarian John I Debranin as its first archbishop, but his successors were Byzantines. The Bulgarian aristocracy and tsar's relatives were given various Byzantine titles and transferred to the Asian parts of the Empire. Despite hardships, the Bulgarian language, literature, and culture survived; surviving period texts refer to and idealize the Bulgarian Empire. Most of the newly conquered territories were included in the themes Bulgaria, Sirmium, and Paristrion.

As the Byzantine Empire declined under Basil's successors, invasions of Pechenegs and rising taxes contributed to increasing discontent, which resulted in several major uprisings in 1040–41, the 1070s, and the 1080s. The initial centre of the resistance was the theme of Bulgaria, in what is now Macedonia, where the massive Uprising of Peter Delyan (1040–41) and the Uprising of Georgi Voiteh (1072) took place. Both were quelled with great difficulty by Byzantine authorities. These were followed by rebellions in Paristrion and Thrace. During the Komnenian Restoration and the temporary stabilisation of the Byzantine Empire in the first half of the 12th century, the Bulgarians were pacified and no major rebellions took place until later in the century.

The disastrous rule of the last Comnenian emperor Andronikos I (r. 1183–85) worsened the situation of the Bulgarian peasantry and nobility. The first act of his successor Isaac II Angelos was to impose an extra tax to finance his wedding. In 1185, two aristocrat brothers from Tarnovo, Theodore and Asen, asked the emperor to enlist them into the army and grant them land, but Isaac II declined and slapped Asen across the face.

Upon their return to Tarnovo, the brothers commissioned the construction of a church dedicated to Saint Demetrius of Salonica. They showed the populace a celebrated icon of the saint, who they claimed had left Salonica to support the Bulgarian cause and called for a rebellion. That act had the desired effect on the religious population, who enthusiastically engaged in a rebellion against the Byzantines. Theodore, the elder brother, was crowned Emperor of Bulgaria under the name Peter IV. Almost all of Bulgaria to the north of the Balkan Mountains—the region known as Moesia—immediately joined the rebels, who also secured the assistance of the Cumans, a Turkic tribe inhabiting lands north of the Danube river. The Cumans soon became an important part of the Bulgarian army, playing a major role in the successes that followed. As soon as the rebellion broke out, Peter IV attempted to seize the old capital of Preslav but failed; he declared Tarnovo the capital of Bulgaria.

From Moesia, the Bulgarians launched attacks in northern Thrace while the Byzantine army was fighting with the Normans, who had attacked Byzantine possessions in the Western Balkans and sacked Salonica, the Empire's second largest city. The Byzantines reacted in mid-1186, when Isaac II organized a campaign to crush the rebellion before it spread further. The Bulgarians had secured the passes but the Byzantine army found its way across the mountains due to a solar eclipse.

The Byzantines successfully attacked the rebels, many of whom fled north of the Danube, making contact with the Cumans. In a symbolic gesture, Isaac II entered Peter's house and took the icon of Saint Demetrius, thus regaining the saint's favour. Still under threat of ambush from the hills, Isaac returned hastily to Constantinople to celebrate his victory. Thus, when the armies of Bulgarians and the Vlachs returned, reinforced with their Cuman allies, they found the region undefended and regained not only their old territory but the whole of Moesia, a considerable step towards the establishment of a new Bulgarian state.

The Emperor now entrusted the war to his uncle, John the sebastocrator, who gained several victories against the rebels but then himself rebelled. He was replaced with the emperor's brother-in-law, John Kantakouzenos, a good strategist but unfamiliar with the guerrilla tactics used by the mountaineers. His army was ambushed, suffering heavy losses, after unwisely pursuing the enemy into the mountains.

In the late autumn of 1186, the Byzantine army marched northwards through Sredets (Sofia). The campaign was planned to surprise the Bulgarians. However, the harsh weather conditions and the early winter postponed the Byzantines and their army had to stay in Sredets during the whole winter.

In the spring of the following year, the campaign was resumed, but the element of surprise was gone and the Bulgarians had taken measures to bar the way to their capital Tarnovo. Instead the Byzantines besieged the strong fortress of Lovech. The siege lasted for three months and was a complete failure. Their only success was the capture of Asen's wife, but Isaac was forced to accept a truce thus de facto recognizing the restoration of the Bulgarian Empire.

The third general in charge of fighting the rebels was Alexius Branas, who, in turn, rebelled and turned on Constantinople. Isaac defeated him with the help of a second brother-in-law, Conrad of Montferrat, but this civil strife had diverted attention from the rebels and Isaac was able to send out a new army only in September 1187. The Byzantines obtained a few minor victories before winter, but the rebels, helped by the Cumans and employing their mountain tactics, still held the advantage.

In the spring of 1187, Isaac attacked the fortress of Lovech, but failed to capture it after a three-month siege. The lands between the Haemus Mons and the Danube were now lost for the Byzantine Empire, leading to the signing of a truce, thus de facto recognising the rule of the Asen and Peter over the territory, leading to the creation of the Second Bulgarian Empire. The Emperor's only consolation was to hold, as hostages, Asen's wife and a certain John (future Kaloyan of Bulgaria), brother of the two new leaders of the Bulgarian state.

In alliance with the Bulgarians and Vlachs, the Cumans are believed to have played a significant role in the uprising led by brothers Asen and Peter of Tarnovo, resulting in victory over Byzantium and the restoration of Bulgaria's independence in 1185. István Vásáry states that without the active participation of the Cumans, the Vlakho-Bulgarian rebels could never have gained the upper hand over the Byzantines, and ultimately without the military support of the Cumans, the process of Bulgarian restoration could never have been realised. The Cuman participation in the creation of the Second Bulgarian Empire in 1185 and thereafter brought about basic changes in the political and ethnic sphere of Bulgaria and the Balkans. The Cumans were allies in the Bulgarian–Latin Wars with emperor Kaloyan of Bulgaria. 

After the siege of Lovech in 1187, the Byzantine Emperor Isaac II Angelos was forced to conclude a truce, thus de facto recognizing the independence of Bulgaria. Until 1189, both sides observed the truce. The Bulgarians used this time to further organize their administration and military. When the soldiers of the Third Crusade reached the Bulgarian lands at Niš, Asen and Peter offered to help the Emperor of the Holy Roman Empire, Frederick I Barbarosa, with a force of 40,000 against the Byzantines. However, the relations between the Crusaders and the Byzantines smoothed, and the Bulgarian proposal was evaded.

The Byzantines prepared a third campaign to avenge the Bulgarian actions. Like the previous two invasions, they managed to overcome the passes of the Balkan mountains. They made a bluff indicating that they would pass near the sea by Pomorie, but instead headed west and passed through the Rishki Pass to Preslav. The Byzantine army next marched westwards to besiege the capital at Tarnovo. At the same time, the Byzantine fleet reached the Danube in order to bar the way of Cuman auxiliaries from the northern Bulgarian territories.

The siege of Tarnovo was unsuccessful. The defense of the city was led by Asen himself and the morale of his troops was very high. The Byzantine morale, on the other hand, was quite low for several reasons: the lack of any military success, heavy casualties and particularly the fact that the soldiers' pay was in arrears. This was used by Asen, who sent an agent in the guise of a deserter to the Byzantine camp. The man told Isaac II that, despite the efforts of the Byzantine navy, an enormous Cuman army had passed the river Danube and was heading towards Tarnovo to relive the siege. The Byzantine Emperor panicked and immediately called for a retreat through the nearest pass.

The Bulgarian Emperor deduced that his opponent would go through the Tryavna Pass. The Byzantine army slowly marched southwards, their troops and baggage train stretching for kilometers. The Bulgarians reached the pass before them and staged an ambush from the heights of a narrow gorge. The Byzantine vanguard concentrated their attack on the centre where the Bulgarian leaders were positioned, but once the two main forces met and hand-to-hand combat ensued, the Bulgarians stationed on the heights showered the Byzantine force below with rocks and arrows. In panic, the Byzantines broke up and began a disorganized retreat, prompting a Bulgarian charge, who slaughtered everyone on their way. Isaac II barely escaped; his guards had to cut a path through their own soldiers, enabling their commander's flight from the rout. The Byzantine historian Niketas Choniates wrote that only Isaac Angelos escaped and most of the others perished.

The battle was a major catastrophe for the Byzantines. The victorious army captured the imperial treasure including the golden helmet of the Byzantine Emperors, the crown and the Imperial Cross which was considered the most valuable possession of the Byzantine rulers - a solid gold reliquary containing a piece of the Holy Cross. It was thrown in the river by a Byzantine cleric but was recovered by the Bulgarians. The victory was very important for Bulgaria. Up to that moment, the official Emperor was Peter IV, but, after the major successes of his younger brother, he was proclaimed Emperor later that year. 

In the next four years, the focus of the war shifted to the south of the Balkan mountains. The Byzantines could not face the fast Bulgarian cavalry which attacked from different directions on a vast area. Towards 1194, Ivan Asen's strategy of swiftly striking in different locations paid off, and he soon took control of the important cities Sofia, Niš and the surrounding areas as well as the upper valley of the Struma River from where his armies advanced deep into Macedonia.

To distract his attention the Byzantines decided to strike in eastern direction. They assembled the Eastern army under its commander Alexios Gidos and the Western army under its Domestic Basil Vatatzes to stop the dangerous rise of Bulgarian power. Near Arcadiopolis in Eastern Thrace they met the Bulgarian army. After a fierce battle the Byzantine armies were annihilated. Most of Gidos's troops perished and he had to flee for his life, while the Western army was fully slaughtered and Basil Vatatzes was killed on the battlefield.

After the defeat Isaac II Angelos forged an alliance with the Hungarian King Bela III against the common enemy. Byzantium had to attack from the south and Hungary was to invade the north-western Bulgarian lands and take Belgrade, Branichevo and eventually Vidin but the plan failed. In March 1195 Isaac II managed to organize a campaign against Bulgaria but he was deposed by his brother Alexios III Angelos and that campaign failed as well.

In the same year, the Bulgarian army advanced deep to the south-west and reached the vicinity of Serres taking many fortresses on its way. During the winter, the Bulgarians retreated to the north but in the next year reappeared and defeated a Byzantine army under the sebastokrator Isaac near the town. In the course of the battle, the Byzantine cavalry was surrounded, suffering heavy casualties, and their commander was captured.

After the Battle of Serres, instead of a triumphal return, the way back to the Bulgarian capital ended tragically. Slightly before reaching Tarnovo, Ivan Asen I was murdered by his cousin Ivanko. The motive for this act is uncertain. Choniates stated, Ivanko wanted to rule "more justly and equitably" than Asan who had "governed everything by the sword". Stephenson concludes, Choniates' words show that Asen had introduced a "reign of terror", intimidating his subjects with the assistance of Cuman mercenaries. Vásáry, however, says the Byzantines encouraged Ivanko to kill Asen. Ivanko attempted to assume control in Tarnovo with Byzantine support, but Peter forced him to flee to the Byzantine Empire.

Theodor (who had been crowned emperor under the name Peter) made him his co-ruler after Asen was murdered in 1196. A year later, Theodor-Peter was also assassinated, and Kaloyan became the sole ruler of Bulgaria.

Kaloyan's expansionist policy brought him into conflict with the Byzantine Empire, Serbia and Hungary. King Emeric of Hungary allowed the papal legate who delivered a royal crown to Kaloyan to enter Bulgaria only at the Pope's demand.

Kaloyan took advantage of the disintegration of the Byzantine Empire after the fall of Constantinople to the crusaders or "Latins" in 1204. He captured fortresses in Macedonia and Thrace and supported the local population's riots against the crusaders. He defeated Baldwin I, Latin emperor of Constantinople, in the Battle of Adrianople on 14 April 1205. Baldwin was captured; he died in Kaloyan's prison. Kaloyan launched new campaigns against the Crusaders and captured or destroyed dozens of their fortresses. He was thereafter known as Kaloyan the Roman slayer, because his troops murdered or captured thousands of Romans. 

Asen was murdered in Tarnovo by the boyar Ivanko in the fall of 1196. Theodor-Peter soon mustered his troops, hurried to the town and laid siege to it. Ivanko sent an envoy to Constantinople, urging the new Byzantine Emperor, Alexios III Angelos, to send reinforcements to him. The emperor dispatched Manuel Kamytzes to lead an army to Tarnovo, but fear of an ambush at the mountain passes led to an outbreak of mutiny and the troops forced him to return. Ivanko realized that he could not defend Tarnovo any more and fled from the town to Constantinople. Theodor-Peter entered Tarnovo. After making his younger brother Kaloyan the ruler of the town, he returned to Preslav.

Theodor-Peter was murdered "in obscure circumstances" in 1197. He was "run through by the sword of one of his countrymen", according to Choniates' record. Historian István Vásáry writes, Theodor-Peter was killed during a riot; Stephenson proposes, the native lords got rid of him, because of his close alliance with the Cumans.

Around this time, he sent a letter to Pope Innocent III, urging him to dispatch an envoy to Bulgaria. He wanted to persuade the pope to acknowledge his rule in Bulgaria. Innocent eagerly entered into correspondence with Kaloyan because the reunification of the Christian denominations under his authority was one of his principal objectives.

Innocent III's envoy arrived in Bulgaria in late December 1199, bringing a letter from the Pope to Kaloyan. Innocent stated that he was informed that Kaloyan's forefathers had come "from the City of Rome". Kaloyan's answer, written in Old Church Slavonic, has not been preserved, but its content can be reconstructed based on his later correspondence with the Holy See. Kaloyan styled himself "Emperor of the Bulgarians and Vlachs", and asserted that he was the legitimate successor of the rulers of the First Bulgarian Empire. He demanded an imperial crown from the Pope and expressed his wish to put the Bulgarian Orthodox Church under the pope's jurisdiction. According to Kaloyan's letter to the Pope, Alexios III was also willing to send an imperial crown to him and to acknowledge the autocephalous (or autonomous) status of the Bulgarian Church.

The Byzantine Emperor Alexios III Angelos made Ivanko the commander of Philippopolis (now Plovdiv in Bulgaria). Ivanko seized two fortresses in the Rhodopi Mountains from Kaloyan, but by 1198 he had made an alliance with him. Cumans and Vlachs from the lands to the north of the river Danube broke into the Byzantine Empire in the spring and autumn of 1199. Choniates, who recorded these events, did not mention that Kaloyan cooperated with the invaders, so it is likely that they crossed Bulgaria without his authorization. Kaloyan captured Braničevo, Velbuzhd, Skopje and Prizren from the Byzantines, most probably in that year, according to historian Alexandru Madgearu. 

The Byzantines captured Ivanko and occupied his lands in 1200. Kaloyan and his Cuman allies launched a new campaign against Byzantine territories in March 1201. He destroyed Constantia (now Simeonovgrad in Bulgaria) and captured Varna. He also supported the rebellion of Dobromir Chrysos and Manuel Kamytzes against Alexios III, but they were both defeated. Roman Mstislavich, prince of Halych and Volhynia, invaded the Cumans' territories, forcing them to return to their homeland in 1201. After the Cuman's retreat, Kaloyan concluded a peace treaty with Alexios III and withdrew his troops from Thrace in late 1201 or in 1202. The Bulgarians secured their new gains and now were able to face the Hungarian threat to the north-west.

Vukan Nemanjić, ruler of Zeta, expelled his brother, Stefan, from Serbia in 1202. Kaloyan gave shelter to Stefan and allowed the Cumans to invade Serbia across Bulgaria. He invaded Serbia himself and captured Niš in the summer of 1203. According to Madgearu he also seized Dobromir Chrysos's realm, including its capital at Prosek. Emeric, King of Hungary, who claimed Belgrade, Braničevo and Niš, intervened in the conflict on Vukan's behalf. The Hungarian army occupied territories which were also claimed by Kaloyan. 

The sack of Constantinople occurred in April 1204 and marked the culmination of the Fourth Crusade. Crusader armies captured, looted, and destroyed parts of Constantinople, then the capital of the Byzantine Empire. After the capture of the city, the Latin Empire (known to the Byzantines as the Frankokratia or the Latin Occupation) was established and Baldwin of Flanders was crowned Emperor Baldwin I of Constantinople in the Hagia Sophia.

After the city's sacking, most of the Byzantine Empire's territories were divided up among the Crusaders. Byzantine aristocrats also established a number of small independent splinter states, one of them being the Empire of Nicaea, which would eventually recapture Constantinople in 1261 and proclaim the reinstatement of the Empire. However, the restored Empire never managed to reclaim its former territorial or economic strength, and eventually fell to the rising Ottoman Empire in the 1453 Siege of Constantinople.

The sack of Constantinople is a major turning point in medieval history. The Crusaders' decision to attack the world's largest Christian city was unprecedented and immediately controversial. Reports of Crusader looting and brutality scandalised and horrified the Orthodox world; relations between the Catholic and Orthodox churches were catastrophically wounded for many centuries afterwards, and would not be substantially repaired until modern times.

The Byzantine Empire was left much poorer, smaller, and ultimately less able to defend itself against the Seljuk and Ottoman conquests that followed; the actions of the Crusaders thus directly accelerated the collapse of Christendom in the east, and in the long run helped facilitate the later Ottoman Conquests of Southeastern Europe.

Dissatisfied with the Pope's decision, Kaloyan sent a new letter to Rome, asking Innocent to send cardinals who could crown him emperor. He also informed the Pope that Emeric of Hungary had seized five Bulgarian bishoprics, asking Innocent to arbitrate in the dispute and determine the boundary between Bulgaria and Hungary. In the letter, he styled himself the "Emperor of the Bulgarians". The Pope did not accept Kaloyan's claim to an imperial crown, but dispatched Cardinal Leo Brancaleoni to Bulgaria in early 1204 to crown him king.

Kaloyan sent envoys to the crusaders who were besieging Constantinople, offering military support to them if "they would crown him king so that he would be lord of his land of Vlachia", according to Robert of Clari's chronicle. However, the crusaders treated him with disdain and did not accept his offer.

The papal legate, Brancaleoni, travelled through Hungary, but he was arrested at Keve on the Hungarian–Bulgarian frontier. Emeric of Hungary urged the cardinal to summon Kaloyan to Hungary and to arbitrate in their conflict. Brancaleoni was only released at the Pope's demand in late September or early October. He consecrated Basil primate of the Church of the Bulgarians and Vlachs on 7 November. Next day, Brancaleone crowned Kaloyan king. In his subsequent letter to the Pope, Kaloyan styled himself as "King of Bulgaria and Vlachia", but referred to his realm as an empire and to Basil as a patriarch.

Taking advantage of the disintegration of the Byzantine Empire, Kaloyan captured former Byzantine territories in Thrace. Initially he attempted to secure a peaceful division of the lands with the crusaders (or "Latins"). He asked Innocent III to prevent them from attacking Bulgaria. However, the crusaders wanted to implement their treaty which divided the Byzantine territories between them, including lands that Kaloyan claimed.

Kaloyan gave shelter to Byzantine refugees and persuaded them to stir up riots in Thrace and Macedonia against the Latins. The refugees, according to Robert of Clari's account, also pledged they would elect him emperor if he invaded the Latin Empire. The Greek burghers of Adrianople (now Edirne in Turkey) and nearby towns rose up against the Latins in early 1205. Kaloyan promised that he would send them reinforcements before Easter. Considering Kaloyan's cooperation with the rebels a dangerous alliance, Emperor Baldwin decided to launch a counter-attack and ordered the withdrawal of his troops from Asia Minor. He laid siege to Adrianople before he could muster all his troops. Kaloyan hurried to the town at the head of an army of more than 14,000 Bulgarian, Vlach and Cuman warriors. A feigned retreat by the Cumans drew the heavy cavalry of the crusaders into an ambush in the marshes north of Adrianople, enabling Kaloyan to inflict a crushing defeat on them on 14 April 1205.

Despite everything, the battle is hard and fought until late in the evening. The main part of the Latin army is eliminated, the knights are defeated and their emperor, Baldwin I, is taken prisoner in Veliko Tarnovo, where he is locked at the top of a tower in the Tsarevets fortress.

Word quickly spread around Europe of the defeat of the knights in the battle of Adrianople. Without a doubt, it was a great shock for the world at the time, due to the fact that the glory of the undefeatable knight army was known to everyone from those in rags to those in riches. Hearing that the knights, whose fame travelled far and wide, who had taken one of the largest cities at the time, Constantinople, the capital whose walls were rumoured to be unbreakable, was devastating for the Catholic world.

Kaloyan's troops pillaged Thrace and Macedonia after his victory over the Latins. He launched a campaign against the Kingdom of Thessalonica, laying siege to Serres in late May. He promised free passage to the defenders, but after their surrender he broke his word and took them captive. He continued the campaign and seized Veria and Moglena (now Almopia in Greece). Most inhabitants of Veria were murdered or captured on his orders. Henry (who still ruled the Latin Empire as regent) launched a counter-invasion against Bulgaria in June. He could not capture Adrianople and a sudden flood forced him to lift the siege of Didymoteicho.

Kaloyan decided to take vengeance of the townspeople of Philippopolis, who had voluntarily cooperated with the crusaders. With the assistance of the local Paulicians, he seized the town and ordered the murder of the most prominent burghers. The commoners were delivered in chains to Vlachia (a loosely defined territory, located to the south of the lower Danube). He returned to Tarnovo after a riot had broken out against him in the second half of 1205 or early 1206. He "subjected the rebels to harsh punishments and novel methods of execution", according to Choniates.

He again invaded Thrace in January 1206. The great victory in the battle of Adrianople was followed by other Bulgarian victories at Serres and Plovdiv. The Latin Empire suffered heavy casualties and in the fall of 1205 the Crusaders tried to regroup and reorganize the remains of their army. Their main forces consisted of 140 knights and several thousand soldiers based in Rusion. He captured Rousion and massacred its Latin garrison. He then destroyed most of the fortresses along the Via Egnatia, as far as Athira. In the whole military operation the Crusaders lost more than 200 knights, many thousands of soldiers and several Venetian garrisons were completely annihilated. 

The massacre and capture of their compatriots outraged the Greeks in Thrace and Macedonia. They realized that Kaloyan was more hostile to them than the Latins. The burghers of Adrianople and Didymoteicho approached Henry of Flanders offering their submission. Henry ccepted the offer and assisted Theodore Branas in taking possession of the two towns. Kaloyan attacked Didymoteicho in June, but the crusaders forced him to lift the siege. Soon after Henry was crowned emperor of the Latins on 20 August, Kaloyan returned and destroyed Didymoteicho. He then laid siege to Adrianople, but Henry forced him to withdraw his troops from Thrace. Henry also broke into Bulgaria and released 20,000 prisoners in October. Boniface, King of Thessalonica, had meanwhile recaptured Serres.

Akropolites recorded that thereafter Kaloyan called himself "Romanslayer", with a clear reference to Basil II who had been known as the "Bulgarslayer" after his destruction of the First Bulgarian Empire.

Kaloyan concluded an alliance with Theodore I Laskaris, Emperor of Nicaea. Laskaris had started a war against David Komnenos, Emperor of Trebizond, who was supported by the Latins. He persuaded Kaloyan to invade Thrace, forcing Henry to withdraw his troops from Asia Minor. Kaloyan laid siege to Adrianople in April 1207, using trebuchets, but the defenders resisted. A month later, the Cumans abandoned Kaloyan's camp, because they wanted to return to the Pontic steppes, which compelled Kaloyan to lift the siege. Innocent III urged Kaloyan to make peace with the Latins, but he did not obey.

Henry concluded a truce with Laskaris in July 1207. He also had a meeting with Boniface of Thessalonica, who acknowledged his suzerainty at Kypsela in Thrace. However, on his way back to Thessalonica, Boniface was ambushed and killed at Mosynopolis on 4 September. According to Geoffrey of Villehardouin local Bulgarians were the perpetrators and they sent Boniface's head to Kaloyan. Robert of Clari and Choniates recorded that Kaloyan had set up the ambush. Boniface was succeeded by his minor son, Demetrius. The child king's mother, Margaret of Hungary, took up the administration of the kingdom. Kaloyan hurried to Thessalonica and laid siege to the town. Kaloyan died during the siege of Thessalonica in October 1207, but the circumstances of his death are uncertain.

After Kaloyan died unexpectedly in October 1207, Boril married his widow, a Cuman princess and seized the throne. His cousin, Ivan Asen, fled from Bulgaria, enabling Boril to strengthen his position. His other kinsmen, Strez and Alexius Slav, refused to acknowledge him as the lawful monarch. Strez took possession of the land between the Struma and Vardar rivers with the support of Stefan Nemanjić of Serbia. Alexius Slav secured his rule in the Rhodope Mountains with the assistance of Henry, the Latin Emperor of Constantinople.

Boril launched unsuccessful military campaigns against the Latin Empire and the Kingdom of Thessalonica during the first years of his reign. He convoked the synod of the Bulgarian Church in early 1211. At the assembly, the bishops condemned the Bogomils for heresy. After an uprising broke out against him in Vidin between 1211 and 1214, he sought the assistance of Andrew II of Hungary, who sent reinforcements to suppress the rebellion. He made peace with the Latin Empire in late 1213 or early 1214. In return for help suppressing a major rebellion in 1211, Boril was forced to cede Belgrade and Braničevo to Hungary. A campaign against Serbia in 1214 also ended in defeat.

In the summer of 1208 the new Emperor of Bulgaria Boril who continued the war of his predecessor Kaloyan against the Latin Empire invaded Eastern Thrace. The Latin Emperor Henry gathered an army in Selymbria and headed to Adrianople. Upon the news of the Crusaders' march, the Bulgarians retreated to better positions in the area of Beroia (Stara Zagora). At night, they sent the Byzantine captives and the spoil to the north of the Balkan Mountains and moved in a battle formation to the Latin camp, which was not fortified.

At dawn, they suddenly attacked and the soldiers on duty put up a fierce fight to gain some time for the rest to prepare for battle. While the Latins were still forming their squads, they suffered heavy casualties, specially by the hands of the numerous and well-experienced Bulgarian archers, who shot those still without their armour. In the meantime the Bulgarian cavalry managed to go round the Latin flanks and managed to attack their main forces.

In the battle that ensued, the Crusaders lost many men and the Emperor himself was lariated, barely escaping from captivity - a knight managed to cut the rope with his sword and protected Henry from the Bulgarian arrows with his heavy armour.

In the end the Crusaders, forced by Bulgarian cavalry, pulled back and retreated to Philippopolis (Plovdiv) in battle formation. The retreat continued for twelve days, in which the Bulgarians closely followed and harassed their opponents inflicting casualties mainly to the Latin rear-guard which was saved several times from complete collapse by the main Crusader forces. However, near Plovdiv the Crusaders finally accepted the battle.

In the spring of 1208, the Bulgarian army invaded Thrace and defeated the Crusaders near Beroe (modern Stara Zagora). Inspired, Boril marched southward and, on 30 June 1208, he encountered the main Latin army. Boril had between 27,000 and 30,000 soldiers, of which 7000 mobile Cuman cavalry, very successful in the Adrianople's battle. The number of Latin army is also around 30,000 fighters total, including several hundred knights. Boril tried to apply the same tactics used by Kaloyan at Adrianople - the mounted archers harassed the Crusaders trying to stretch their line to lead them towards the main Bulgarian forces. The knights, however, had learned the bitter lesson from Adrianople and did not repeat the same mistake. Instead, they organized a trap and attacked the detachment which was personally commanded by the Tsar, who had only 1,600 men and could not withstand the assault. Boril fled and the whole Bulgarian army pulled back.

The Bulgarians knew that the enemy would not chase them into the mountains so they retreated towards one of the eastern passes of the Balkan Mountains, Turia. The Crusaders who followed the Bulgarian army were attacked in a hilly country near the contemporary village of Zelenikovo by the Bulgarian rear guard and, after a bitter fight, were defeated. However, their formation did not collapse as the main Latin forces arrived and the battle continued for a very long time until the Bulgarians retreated to the north after the bulk of their army had safely passed through the mountains. The Crusaders then retreated to Philippopolis.

A papal legate (identified as Pelagius of Albano) came to Bulgaria in the summer of 1213. He continued his journey towards Constantinople, implying that his mediation contributed to the subsequent reconciliation between Boril and Henry. Boril desired peace because he had already realised that he would be unable to regain the Thracian territories lost to the Latin Empire; Henry wanted peace with Bulgaria in order to resume his war against Emperor Theodore I Laskaris. After lengthy negotiations, Henry married Boril's stepdaughter (whom modern historians wrongly call Maria) in late 1213 or early 1214.

In early 1214, Boril offered the hand of his unnamed daughter to Andrew II of Hungary's son and heir, Béla. Madgearu says he also renounced the lands that Andrew had claimed from Bulgaria (including Braničevo). In an attempt to conquer new lands, Boril launched an invasion of Serbia, laying siege to Niš in 1214, aided by troops sent by Henry. At the same time, Strez invaded Serbia from the south, although he was killed during his campaign. Boril was unable to seize Niš however, due to conflicts between the Bulgarian and Latin troops. Conflicts between Boril and the Latin troops prevented them from capturing the town.

Boril was deprived of his two principal allies by 1217, as Latin Emperor Henry died in July 1216, and Andrew II left Hungary to lead a crusade to the Holy Land in 1217; this position of weakness enabled his cousin, Ivan Asen, to invade Bulgaria. As a result of the growing discontent with his policy, Boril was overthrown in 1218 by Ivan Asen II, son of Ivan Asen I, who had lived in exile after Kaloyan's death.

Boril was beaten by Ivan Asen in battle, and forced to withdraw to Tarnovo, which Ivan's troops laid siege to. The Byzantine historian, George Akropolites, stated that the siege lasted "for seven years", however most modern historians believe that it was actually seven months. After Ivan Asen's troops seized the town in 1218, Boril attempted to flee, but was captured and blinded. No further information was recorded about Boril's fate.

The first decade of Ivan Asen's rule is poorly documented. Andrew II of Hungary reached Bulgaria during his return from the Fifth Crusade in late 1218. Ivan Asen did not allow the king to cross the country until Andrew promised to give his daughter, Maria, in marriage to him. Maria's dowry included the region of Belgrade and Braničevo, the possession of which had been disputed by the Hungarian and Bulgarian rulers for decades.

When Robert of Courtenay, the newly elected Latin Emperor, was marching from France towards Constantinople in 1221, Ivan Asen accompanied him across Bulgaria. He also supplied the emperor's retinue with food and fodder. The relationship between Bulgaria and the Latin Empire remained peaceful during the reign of Robert. Ivan Asen also made peace with the ruler of Epirus, Theodore Komnenos Doukas, who was one of the principal enemies of the Latin Empire. Theodore's brother, Manuel Doukas, married Ivan Asen's illegitimate daughter, Mary, in 1225. Theodore who regarded himself the lawful successor of the Byzantine emperors was crowned emperor around 1226.

Relationship between Bulgaria and Hungary deteriorated in the late 1220s. Shortly after the Mongols inflicted a serious defeat on the united armies of the Rus' princes and Cuman chieftains in the Battle of the Kalka River in 1223, a leader of a western Cuman tribe, Boricius, converted to Catholicism in the presence of Andrew II's heir and co-ruler, Béla IV. Pope Gregory IX stated in a letter that those who had attacked the converted Cumans were also the enemies of the Roman Catholic Church, possibly in reference to a previous attack by Ivan Asen, according to Madgearu.

The control of the trade on the Via Egnatia enabled Ivan Asen to implement an ambitious building program in Tarnovo and struck gold coins in his new mint in Ohrid. He started negotiations about the return of the Bulgarian Church to Orthodoxy after the barons of the Latin Empire had elected John of Brienne regent for Baldwin II in 1229.

Around 1221–1222 Emperor Ivan Asen II of Bulgaria made an alliance with Theodore Komnenos Doukas, the ruler of Epirus. Secured by the treaty, Theodore managed to conquer Thessalonica from the Latin Empire, as well as lands in Macedonia including Ohrid, and establish the Empire of Thessalonica. After the death of the Latin emperor Robert of Courtenay in 1228, Ivan Asen II was considered the most probable choice for regent of Baldwin II. Theodore thought that Bulgaria was the only obstacle left on his way to Constantinople and in the beginning of March 1230 he invaded the country, breaking the peace treaty and without a declaration of war.

Theodore Komnenos summoned a large army, including western mercenaries. He was so confident of victory that he took the whole royal court with him, including his wife and children. His army moved slowly and plundered the villages on its way. When the Bulgarian tsar learned that the state was invaded, he gathered a small army of a few thousand men including Cumans and quickly marched southwards. In four days the Bulgarians covered a distance three times longer than Theodore's army had travelled in a week.

On 9 March, the two armies met near the village of Klokotnitsa. It is said that Ivan Asen II ordered the broken mutual protection treaty to be stuck on his spear and used as a flag. He was a good tactician and managed to surround the enemy, who were surprised to meet the Bulgarians so soon. The battle continued until sunset. Theodore's men were completely defeated, only a small force under his brother Manuel managed to escape from the battlefield. The rest were killed in the battle or captured, including the royal court of Thessalonica and Theodore himself. 

Ivan Asen II immediately released the captured soldiers without any conditions and the nobles were taken to Tarnovo. His fame for being a merciful and just ruler went ahead of his march to the lands of Theodore Komnenos and Theodore's recently conquered territories in Thrace and Macedonia were regained by Bulgaria without resistance. 

Bulgaria became the dominant power of Southeastern Europe after the Battle of Klokotnitsa. Ivan's troops swept into Theodore's lands and conquered dozens of Epirote towns. They captured Ohrid, Prilep and Serres in Macedonia, Adrianople, Demotika and Plovdiv in Thrace and also occupied Great Vlachia in Thessaly. Alexius Slav's realm in the Rhodope Mountains was also annexed. Ivan Asen placed Bulgarian garrisons in the important fortresses and appointed his own men to command them and to collect the taxes, but local officials continued to administer other places in the conquered territories. He replaced the Greek bishops with Bulgarian prelates in Macedonia. He made generous grants to the monasteries on Mount Athos during his visit there in 1230, but he could not persuade the monks to acknowledge the jurisdiction of the primate of the Bulgarian Church. His son-in-law, Manuel Doukas, took control of the Empire of Thessaloniki. The Bulgarian troops also made a plundering raid against Serbia, because Stefan Radoslav, King of Serbia, had supported his father-in-law, Theodore, against Bulgaria.

Ivan Asen's conquests secured the Bulgarian control of the Via Egnatia (the important trade route between Thessaloniki and Durazzo). He established a mint in Ohrid which started to struck gold coins. His growing revenues enabled him to accomplish an ambitious building program in Tarnovo. The Church of the Holy Forty Martyrs, with its facade decorated with ceramic tiles and murals, commemorated his victory at Klokotnitsa. The imperial palace on the Tsaravets Hill was enlarged. A memorial inscription on one of the columns of the Church of the Holy Forty Martyrs recorded Ivan Asen's conquests. It referred to him as the "tsar of the Bulgarians, Greeks and other countries", implying that he was planning to revive the Byzantine Empire under his rule. He also styled himself emperor in his letter of grant to the Vatopedi Monastery on Mount Athos and in his diploma about the privileges of the Ragusan merchants. Imitating the Byzantine emperors, he sealed his charters with gold bulls. One of his seals portrayed him wearing imperial insignia, also revealing his imperial ambitions.

News about John of Brienne's election to the regency in the Latin Empire outraged Ivan Asen. He sent envoys to the Ecumenical Patriarch Germanus II to Nicaea to start negotiations about the position of the Bulgarian Church. Pope Gregory IX urged Andrew II of Hungary to launch a crusade against the enemies of the Latin Empire on 9 May 1231, most probably in reference to Ivan Asen's hostile actions, according to Madgearu. Béla IV of Hungary invaded Bulgaria and captured Belgrade and Braničevo in late 1231 or in 1232, but the Bulgarians reconquered the lost territories already in the early 1230s. The Hungarians seized the Bulgarian fortress at Severin (now Drobeta-Turnu Severin in Romania) to the north of the Lower Danube and established a border province, known as the Banate of Szörény, to prevent the Bulgarians from expanding to the north.

Ivan Asen and Vatatzes made an alliance against the Latin Empire. The Bulgarian troops conquered the territories to the west of the Maritsa, while the Nicean army seized the lands to the east of the river. They laid siege to Constantinople, but John of Brienne and the Venetian fleet forced them to lift the siege before the end of 1235. Early next year, they again attacked Constantinople, but the second siege ended in a new failure.

A new Mongol invasion of Europe forced thousands of Cumans to flee from the steppes in the summer of 1237. Istvan Vassary states that after the Mongol conquest, "A large-scale westward migration of the Cumans began." Certain Cumans also moved to Anatolia, Kazakhstan and Turkmenistan. In the summer of 1237 the first wave of this Cuman exodus appeared in Bulgaria. The Cumans crossed the Danube, and this time Tsar Ivan Asen II could not tame them, as he had often been able to do earlier; the only possibility left for him was to let them march through Bulgaria in a southerly direction. They proceeded through Thrace as far as Hadrianoupolis and Didymotoichon, plundering and pillaging the towns and the countryside, just as before. The whole of Thrace became, as Akropolites put it, a "Scythian desert."

Ivan Asen sent envoys to Hungary before May 1240, most probably because he wanted to forge a defensive alliance against the Mongols. The Mongols' authority expanded as far as the Lower Danube after they captured Kiev on 6 December 1240. The Mongol expansion forced dozens of dispossessed Rus' princes and boyars to flee to Bulgaria. The Cumans who had settled in Hungary also fled to Bulgaria after their chieftain, Köten, was murdered in March 1241. According to a biography of the Mamluk sultan, Baibars, who was descended from a Cuman tribe, this tribe also sought asylum in Bulgaria after the Mongol invasion. The same source adds, that "A.n.s.khan, the king of Vlachia", who is associated with Ivan Asen by modern scholars, allowed the Cumans to settle in a valley, but he soon attacked and killed or enslaved them. Madgearu writes that Ivan Asen most probably attacked the Cumans because he wanted to prevent them from pillaging Bulgaria.

Ivan Asen II was succeeded by his infant son Kaliman I. Despite the initial success against the Mongols, the regency of the new emperor decided to avoid further raids and chose to pay them tribute instead. The lack of a strong monarch and increasing rivalries among the nobility caused Bulgaria to rapidly decline. Its main rival Nicaea avoided Mongol raids and gained power in the Balkans. After the death of 12-year-old Kaliman I in 1246, the throne was succeeded by several short-reigned rulers. The weakness of the new government was exposed when the Nicaean army conquered large areas in southern Thrace, the Rhodopes, and Macedonia—including Adrianople, Tsepina, Stanimaka, Melnik, Serres, Skopje, and Ohrid—meeting little resistance. The Hungarians also exploited Bulgarian weakness, occupying Belgrade and Braničevo. 

During the Mongol invasion of Europe, Mongol tumens led by Batu Khan and Kadan invaded Serbia and then Bulgaria in the spring of 1242 after defeating the Hungarians at the battle of Mohi and ravaging the Hungarian regions of Croatia, Dalmatia and Bosnia.

Having passed through Bosnian and Serb lands, Kadan joined up with the main army under Batu in Bulgaria, probably towards the end of spring. There is archaeological evidence of widespread destruction in central and northeastern Bulgaria around 1242. There are several narrative sources of the Mongol invasion of Bulgaria, but none is detailed and they present distinct pictures of what transpired. It is clear, though, that two forces entered Bulgaria at the same time: Kadan's from Serbia and another, led by Batu himself or Bujek, from across the Danube.

Initially, the troops of Kadan moved south along the Adriatic Sea into Serbian territory. Then, turning east, it crossed the centre of the country—plundering as it went—and entered Bulgaria, where it was joined by the rest of the army under Batu. The campaigning in Bulgaria probably happened mainly in the north, where archaeology yields evidence of destruction from this period. The Mongols did, however, cross Bulgaria to attack the Latin Empire to its south before withdrawing completely. Bulgaria was forced to pay tribute to the Mongols, and this continued thereafter.

Some historians believe that Bulgaria escaped major destruction by accepting Mongol suzerainty, while others have argued that the evidence of Mongol raiding is strong enough that there can have been no escaping. In any case, the campaign of 1242 brought the frontier of the authority of the Golden Horde (Batu's command) to the Danube, where it remained for some decades. The Venetian doge and historian Andrea Dandolo, writing a century later, says that the Mongols "occupied" the kingdom of Bulgaria during the 1241–42 campaign.

Michael II Asen was the son of Ivan Asen II and Irene Komnene Doukaina. He succeeded his half-brother, Kaliman I Asen. His mother or other relative must have ruled Bulgaria during his minority.

John III Doukas Vatatzes, Emperor of Nicaea, and Michael II of Epirus invaded Bulgaria shortly after Michael's ascension. Vatatzes captured the Bulgarian fortresses along the river Vardar; Michael of Epirus took possession of western Macedonia. In alliance with the Republic of Ragusa, Michael II Asen broke into Serbia in 1254, but he could not occupy Serbian territories. After Vatatzes died, he reconquered most territories lost to Nicea, but Vatatzes's son and successor, Theodore II Laskaris, launched a successful counter-offensive, forcing Michael to sign a peace treaty. Shortly after the treaty, discontented boyars (noblemen) murdered Michael.

Vatatzes died on 4 November 1254. Taking advantage of the absence of significant Nicene forces, Michael broke into Macedonia and reconquered the lands lost to Vatatzes in 1246 or 1247. The Byzantine historian, George Akropolites, recorded that the Bulgarian-speaking local inhabitants supported Michael's invasion because they wanted to shake off the "yoke of those who spoke another language".

Theodore II Laskaris, launched a counter-invasion in early 1255. When referring to the new war between Nicea and Bulgaria, Rubruck described Michael as "a mere lad whose power has been eroded" by the Mongols. Michael could not resist the invasion and the Nicene troops captured Stara Zagora. It was only the harsh weather that prevented Theodore's army from continuing the invasion. The Nicene troops resumed their attack in the spring and occupied most fortresses in the Rhodope Mountains. 

Michael broke into the European territory of the Empire of Nicea in the spring of 1256. He pillaged Thrace near Constantinople, but the Nicene army defeated his Cuman troops. He asked his father-in-law to mediate a reconciliation between Bulgaria and Nicea in June. Theodore agreed to sign a peace treaty only after Michael acknowledged the loss of the lands that he had claimed for Bulgaria. The treaty determined the upper course of the river Maritsa as the border between the two countries. The peace treaty outraged many boyars (noblemen) who decided to replace Michael with his cousin, Kaliman Asen. Kaliman and his allies attacked the Tsar who died from his wounds in late 1256 or early 1257.

Constantine Tih mounted the Bulgarian throne after the death of Michael II Asen, but the circumstances of his ascension are obscure. Michael Asen was murdered by his cousin, Kaliman in late 1256 or early 1257. Before long, Kaliman was also killed, and the male line of the Asen dynasty died out. 

Rostislav Mikhailovich, Duke of Macsó (who was Michael and Kaliman's father-in-law), and the boyar Mitso (who was Michael's brother-in-law), laid claim to Bulgaria. Rostislav captured Vidin, Mitso held sway over southeastern Bulgaria, but none of them could secure the support of the boyars who controlled Tarnovo. The latter offered the throne Constantine who accepted the election. 

Constantine divorced his first wife, and married Irene Doukaina Laskarina in 1258. Irene was the daughter of Theodore II Laskaris, Emperor of Nicaea, and Elena of Bulgaria, a daughter of Ivan Asen II of Bulgaria. The marriage with a descendant of the Bulgarian royal family strengthened his position. He was thereafter called Konstantin Asen. The marriage also forged an alliance between Bulgaria and Nicaea, which was confirmed one or two years later, when the Byzantine historian and official George Akropolites came to Tarnovo. 

Rostislav Mikhailovich invaded Bulgaria with Hungarian assistance in 1259. In the following year, Rostislav left his duchy to join the campaign of his father-in-law, Béla IV of Hungary, against Bohemia. Taking advantage of Rostislav's absence, Konstantin broke into his realm and reoccupied Vidin. He also sent an army to attack the Banate of Severin, but the Hungarian commander, Lawrence, fought the invaders off.

The Bulgarian invasion of Severin outraged Béla IV. Soon after he concluded a peace treaty with Ottokar II of Bohemia in March 1261, Hungarian troops stormed into Bulgaria under the command of Béla IV's son and heir, Stephen. They captured Vidin and besieged Lom on the Lower Danube, but they were unable to bring Konstantin to a pitched battle, because he withdrew to Tarnovo. The Hungarian army left Bulgaria before the end of the year, but the campaign restored northwestern Bulgaria to Rostislav.

Konstantin's minor brother-in-law, John IV Laskaris, was dethroned and blinded by his former guardian and co-ruler, Michael VIII Palaiologos, before the end of 1261. Michael VIII's army had occupied Constantinople already in July, thus the coup made him the sole ruler of the restored Byzantine Empire. The rebirth of the empire changed the traditional relations between the powers of the Balkan Peninsula. Furthermore, Konstantine's wife decided to take vengeance of her brother's mutilation and persuaded Konstantine to turn against Michael.

Mitso Asen, former emperor, who still held southeastern Bulgaria, made an alliance with the Byzantines, but another powerful nobleman, Jacob Svetoslav, who had taken control of the southwestern region, was loyal to Konstantine. Benefiting from a war between the Byzantine Empire, the Republic of Venice, Achaea and Epirus, Konstantine invaded Thrace and captured Stanimaka and Philippopolis in the autumn of 1262. Mitso was also forced to flee to Mesembria (now Nesebar in Bulgaria). After Konstantine laid siege to the town, Mitso sought assistance from the Byzantines, offering to surrender Mesembria to them in exchange for landed property in the Byzantine Empire. Michael VIII accepted the offer and sent Michael Glabas Tarchaneiotes to help Mitso in 1263.

A second Byzantine army stormed into Thrace and recaptured Stanimaka and Philippopolis. After seizing Mesembria from Mitso, Glabas Tarchaneiotes continued his campaign along the Black Sea and occupied Agathopolis, Sozopolis and Anchialos. Meanwhile, the Byzantine fleet took control of Vicina and other ports at the Danube Delta. Glabas Tarchaneiotes attacked Jacob Svetoslav who could only resist with Hungarian assistance, thus he accepted Béla IV's suzerainty.

As a consequence of the war with the Byzantines, by the end of 1263, Bulgaria lost significant territories to his two principal enemies, the Byzantine Empire and Hungary. Konstantin could only seek assistance from the Tatars of the Golden Horde to put an end to his isolation. The Tatar khans had been the overlords of the Bulgarian monarchs for almost two decades, although their rule was only formal. A former Sultan of Rum, Kaykaus II, who had been imprisoned at Michael VIII's order, also wanted to regain his throne with the Tatars' help. One of his uncles was a prominent leader of the Golden Horde and he sent messages to him to persuade the Tatars to invade the Byzantine Empire with Bulgarian assistance.

Thousands of Tatars crossed the frozen Lower Danube to invade the Byzantine Empire in late 1264. Konstantin soon joined them, although he had fallen from a horse and broken his leg. The united Tatar and Bulgarian armies launched a sudden attack against Michael VIII who was returning from Thessaly to Constantinople, but they could not capture the emperor. Konstantin laid siege the Byzantine fortress of Ainos (now Enez in Turkey), forcing the defenders to surrender. The Byzantines also agreed to release Kaykaus (who soon left for the Golden Horde), but his family was kept imprisoned even thereafter.

Charles I of Anjou and Baldwin II, the dispossessed Latin emperor of Constantinople, made an alliance against the Byzantine Empire in 1267. To prevent Bulgaria from joining the anti-Byzantine coalition, Michael VIII offered his niece, Maria Palaiologina Kantakouzene, to the widowed Konstantin in 1268. The emperor also pledged that he would return Mesembria and Anchialos to Bulgaria as her dowry if she gave birth to a son. Konstantin married Maria, but Michael VIII broke his promise and did not renounce the two towns after the birth of Konstantin and Maria's son, Michael. Outraged by the emperor's betrayal, Konstantin sent envoys to Charles to Naples in September 1271. The negotiations continued during the following years, showing that Konstantin was willing to support Charles against the Byzantines.

Konstantin broke into Thrace in 1271 or 1272, but Michael VIII persuaded Nogai, the dominant figure in the westernmost territory of the Golden Horde, to invade Bulgaria. The Tatars plundered the country, forcing Konstantin to return and abandon his claim to the two towns. Nogai set up his capital in Isaccea near the Danube Delta, thus he could easily attack Bulgaria. Konstantin had been seriously injured after a riding accident and could not move without assistance, because he was paralyzed from the waist down. The paralyzed Konstantin could not prevent Nogai's Tatars from making regular plundering raids against Bulgaria.

Due to the expensive and unsuccessful wars, repeated Mongol raids, and economic instability, the government was faced with a revolt in 1277. The Uprising of Ivaylo was a rebellion of the Bulgarian peasantry against the incompetent rule of Emperor Constantine Tikh and the Bulgarian nobility. The revolt was fuelled mainly by the failure of the central authorities to confront the Mongol menace in north-eastern Bulgaria. The Mongols had looted and ravaged the Bulgarian population for decades, especially in the region of Dobrudzha. The weakness of the state institutions was due to the accelerating feudalisation of the Second Bulgarian Empire.

The peasants' leader Ivaylo, said to have been a swineherd by the contemporary Byzantine chroniclers, proved to be a successful general and charismatic leader. In the first months of the rebellion, he defeated the Mongols and the emperor's armies, personally slaying Constantine Tikh in battle. Later, he made a triumphant entry in the capital Tarnovo, married Maria Palaiologina Kantakouzene, the emperor's widow, and forced the nobility to recognize him as emperor of Bulgaria.

The Byzantine Emperor Michael VIII Palaiologos decided to make use of the instability in Bulgaria. He sent an army to impose his ally Ivan Asen III on the throne. Ivan Asen III gained control of the area between Vidin and Cherven. Ivailo was besieged by the Mongols at Drastar (Silistra) and the nobility in the capital Tarnovo accepted Ivan Asen III for Emperor.

In the same year, however, Ivailo managed to make a breakthrough in Drastar and headed for the capital. In order to help his ally, Michael VIII sent a 10,000-strong army towards Bulgaria under Murin. When Ivailo learned of that campaign he abandoned his march to Tarnovo. Although his troops were outnumbered, the Bulgarian leader attacked Murin in the Kotel Pass on 17 July 1279 and the Byzantines were completely routed. Many of them perished in the battle, while the rest were captured and later killed by orders from Ivailo. After the defeat Michael VIII sent another army of 5,000 troops under Aprin but it was also defeated by Ivailo before reaching the Balkan Mountains. Without support, Ivan Asen III had to flee to Constantinople. 

The Byzantine Emperor Michael VIII Palaiologos tried to exploit this situation and intervened in Bulgaria. He sent Ivan Asen III, son of the former Emperor Mitso Asen, to claim the Bulgarian throne at the head of a large Byzantine army. Simultaneously, Michael VIII incited the Mongols to attack from the north, forcing Ivaylo to fight on two fronts. Ivaylo was defeated by the Mongols and besieged in the important fortress of Drastar. In his absence, the nobility in Tarnovo opened the gates to Ivan Asen III. However, Ivaylo broke the siege and Ivan Asen III fled back to the Byzantine Empire. Michael VIII sent two large armies, but they were both defeated by the Bulgarian rebels in the Balkan mountains.

Meanwhile, the nobility in the capital had proclaimed as emperor one of their own, the magnate George Terter I. Surrounded by enemies and with diminishing support due to the constant warfare, Ivaylo fled to the court of the Mongol warlord Nogai Khan to seek aid, but was eventually murdered. The legacy of the rebellion endured both in Bulgaria and in Byzantium. 

The continued success of Ivaylo against Byzantine reinforcements led Ivan Asen III to flee the capital and escape to the Byzantine Empire, while George Terter I seized power as emperor in 1280. With the threat from Ivaylo and Ivan Asen III removed, George Terter I made an alliance with King Charles I of Sicily, with Stefan Dragutin of Serbia, and with Thessaly against Michael VIII Palaeologus of the Byzantine Empire in 1281. The alliance failed as Charles was distracted by the Sicilian Vespers and the secession of Sicily in 1282, while Bulgaria was ravaged by the Mongols of the Golden Horde under Nogai Khan. Seeking Serbian support, George Terter I engaged his daughter Anna to the Serbian king Stefan Uroš II Milutin in 1284.

Since the death of the Byzantine Emperor Michael VIII Palaiologos in 1282, George Terter I re-opened negotiations with the Byzantine Empire and sought the return of his first wife. This was eventually accomplished by treaty, and the two Marias exchanged places as empress and hostage. Theodore Svetoslav also returned to Bulgaria after a successful mission of Patriarch Joachim III and was made co-emperor by his father, but after another Mongol invasion in 1285, he was sent off as a hostage to Nogai Khan. Theodore Svetoslav's other sister, Helena, was also sent to the Horde, where she married Nogai's son Chaka.

The reasons for his exile are not very clear. According to George Pachymeres, after an attack by Nogai Khan on Bulgaria, George Terter was removed from the throne and then traveled to Adrianople. The Byzantine Emperor Andronikos II Palaiologos at first refused to receive him, perhaps fearing complications with the Mongols, and George Terter was kept waiting in wretched conditions in the vicinity of Adrianople. The former Bulgarian emperor was eventually sent to live in Anatolia. George Terter I passed the next decade of his life in obscurity. 

The reign of Smilec has been considered the height of Mongol overlordship in Bulgaria. Nevertheless, Mongol raids may have continued, as in 1297 and 1298. Since these raids pillaged parts of Thrace (then entirely in Byzantine hands), perhaps Bulgaria was not one of their objectives. In fact, in spite of the usually pro-Byzantine policy of Nogai, Smilec was quickly involved in an unsuccessful war against the Byzantine Empire at the beginning of his reign.

About 1296/1297 Smilec married his daughter Theodora to the future Serbian King Stefan Uroš III Dečanski, and this union produced the Serbian king and later emperor Stefan Uroš IV Dušan.

In 1298 Smilec disappears from the pages of history, apparently after the beginning of Chaka's invasion. He may have been killed by Chaka or died of natural causes while the enemy advanced against him. Smilec was briefly succeeded by his young son Ivan II.

Chaka was the son of the Mongol leader Nogai Khan by a wife named Alaka. Sometime after 1285 Chaka married a daughter of George Terter I of Bulgaria, named Elena. In the late 1290s, Chaka supported his father Nogai in a war against the legitimate khan of the Golden Horde Toqta, but Toqta was victorious and defeated and killed Nogai in 1299.

At about the same time Chaka had led his supporters into Bulgaria, intimidated the regency for Ivan II into fleeing the capital, and imposed himself as ruler in Tărnovo in 1299. It is not completely certain whether he reigned as Emperor of Bulgaria or simply acted as the overlord of his brother-in-law Theodore Svetoslav. He is accepted as a ruler of Bulgaria by Bulgarian historiography.

Chaka did not long enjoy his new position of power, as the armies of Toqta followed him into Bulgaria and besieged Tărnovo. Theodore Svetoslav, who had been instrumental in assisting Chaka's seizure of power, organized a plot in which Chaka was deposed and strangled in prison in 1300.

The reign of Theodore Svetoslav is connected with the internal stabilization and pacification of the country, the end of Mongol control of Tarnovo, and the recovery of portions of Thrace lost to the Byzantine Empire since the wars against Ivaylo of Bulgaria.

Theodore Svetoslav pursued a ruthless course of action, punishing all who stood in his way, including his former benefactor, Patriarch Joachim III, who was accused of treason and executed. In the face of the new emperor's brutality, some noble factions sought to replace him with other claimants to the throne, backed by Andronikos II. A new claimant appeared in the person of the sebastokratōr Radoslav Voïsil from Sredna Gora, a brother of the former emperor Smilets, who was defeated, and captured by Theodore Svetoslav's uncle, the despotēs Aldimir (Eltimir), at Krăn in about 1301.

Another pretender was the former emperor Michael Asen II, who unsuccessfully tried to advance into Bulgaria with a Byzantine army in about 1302. Theodore Svetoslav exchanged thirteen high-ranking Byzantine officers captured on Radoslav's defeat for his father George Terter I, whom he settled in a life of luxury in an unidentified city.

As a consequence of his victories, Theodore Svetoslav felt secure enough to move on to the offensive by 1303 and captured the fortresses of northeastern Thrace, including Mesembria (Nesebăr), Anchialos (Pomorie), Sozopolis (Sozopol), and Agathopolis (Ahtopol) in 1304. 

When Theodore Svetoslav was crowned Emperor of Bulgaria in 1300, he sought revenge for the Tatar attacks on the state in the previous 20 years. The traitors were punished first, including Patriarch Joachim III, who was found guilty of helping the enemies of the crown. Then the tsar turned to Byzantium, which had inspired the Tatar invasions and had managed to conquer many Bulgarian fortresses in Thrace. In 1303, his army marched southwards and regained many towns. In the following year the Byzantines counter-attacked and the two armies met near the Skafida river.

The Byzantines had an advantage in the beginning and managed to push the Bulgarians across the river. They were so infatuated with the chase of the retreating soldiers that they crowded on the bridge, which had been sabotaged before the battle by the Bulgarians, and broke down. The river was very deep at that place and many Byzantine soldiers panicked and drowned, which helped the Bulgarians snatch victory. After the victory, the Bulgarians captured a lot of Byzantine soldiers and according to custom the ordinary people were released and only the nobles were held for ransom. 

Michael Asen III was the founder of the last ruling dynasty of the Second Bulgarian Empire, the Shishman dynasty. After he was crowned, however, Michael used the name Asen to emphasize his connection with the Asen dynasty, the first one to rule over the Second Empire.

An energetic and ambitious ruler, Michael Shishman led an aggressive but opportunistic and inconsistent foreign policy against the Byzantine Empire and the Kingdom of Serbia, which ended in the disastrous Battle of Velbazhd that claimed his own life. He was the last medieval Bulgarian ruler who aimed at military and political hegemony of the Bulgarian Empire over the Balkans and the last one who attempted to seize Constantinople. He was succeeded by his son Ivan Stephen and later by his nephew Ivan Alexander, who reversed Michael Shishman's policy by forming an alliance with Serbia.

After 1328 Andronikos III won and deposed his grandfather. Serbia and the Byzantines entered a period of bad relations, closer to the state of undeclared war. Previously, in 1324, he divorced and ousted his wife and Stefan's sister Anna Neda, and married Andronikos III's sister Theodora. During that time the Serbs captured some important towns such as Prosek and Prilep and even besieged Ohrid (1329).

Both Empires(Byzantine and Bulgarian) were seriously worried about the fast growth of Serbia and on 13 May 1327 settled a clearly anti-Serb peace treaty. After another meeting with Andronikos III in 1329, the rulers decided to invade their common enemy; Michael Asen III prepared for joint military operations against Serbia. The plan included the thorough elimination of Serbia and its partition between Bulgaria and the Byzantine Empire. 

The bulk of the two armies camped in the vicinity of Velbazhd, but both Michael Shishman and Stefan Dečanski expected reinforcements and from 24 July they began negotiations which ended with a one-day truce. The Emperor had other problems which influenced his decision for the truce: the army supply units had not yet arrived and the Bulgarians were short on food. Their troops scattered around the country and the nearby villages to search for provisions. Meanwhile, receiving a sizable reinforcement, 1,000 heavily armed Catalan horsemen mercenaries, led by his son Stefan Dušan during the night, the Serbs broke their word and attacked the Bulgarian army. early on 28 July 1330 and caught the Bulgarian army by surprise. The Serbian victory shaped the balance of power in Balkans for the next two decades. 

The long reign of Ivan Alexander is considered a transitional period in Bulgarian medieval history. Ivan Alexander began his rule by dealing with internal problems and external threats from Bulgaria's neighbours, the Byzantine Empire and Serbia, as well as leading his empire into a period of economic recovery and cultural and religious renaissance.

However, the emperor was later unable to cope with the mounting incursions of Ottoman forces, Hungarian invasions from the northwest and the Black Death. In an ill-fated attempt to combat these problems, he divided the country between his two sons, thus forcing it to face the imminent Ottoman conquest weakened and divided.

In the summer of the same year, the Byzantines gathered an army and without a declaration of war advanced towards Bulgaria, looting and plundering the villages on their way. The Emperor faced the Bulgarians at the village of Rusokastro. 

Ivan Alexander had troops of 8,000 while the Byzantines were only 3,000. There were negotiations between the two rulers but the Bulgarian emperor deliberately prolonged them because he was awaiting reinforcements. In the night of July 17 they finally arrived in his camp (3,000 cavalrymen) and he decided to attack the Byzantines the next day. Andronikos III Palaiologos had no choice but to accept the fight.

The battle began at six in the morning and continued for three hours. The Byzantines tried to prevent the Bulgarian cavalry from surrounding them, but their manoeuvre failed. The cavalry moved around the first Byzantine line, leaving it for the infantry and charged the rear of their flanks. After a fierce fight the Byzantines were defeated, abandoned the battlefield and took refuge in Rusokastro. The Bulgarian army surrounded the fortress and at noon on the same day Ivan Alexander sent envoys to continue the negotiations. The Bulgarians recovered their lost territory in Thrace and strengthened the position of their empire. This was the last major battle between Bulgaria and Byzantium as their seven-century rivalry for domination of the Balkans was soon to come to an end, after the fall of the two Empires under Ottoman domination.

In 1341–1347 the Byzantine Empire was plunged into a protracted civil war between the regency for Emperor John V Palaiologos under Anna of Savoy and his intended guardian John VI Kantakouzenos. The neighbours of the Byzantines took advantage of the civil war, and while Stefan Uroš IV Dušan of Serbia sided with John VI Kantakouzenos, Ivan Alexander backed John V Palaiologos and his regency. Although the two Balkan rulers picked opposite sides in the Byzantine civil war, they maintained their alliance with each other. As the price for Ivan Alexander's support, the regency for John V Palaiologos ceded him the city of Philippopolis (Plovdiv) and nine important fortresses in the Rhodope Mountains in 1344. This peaceful turnover constituted the last major success of Ivan Alexander's foreign policy.

By the second half of the 1340s, little remained of Ivan Alexander's initial successes. John VI Kantakouzenos' Turkish allies pillaged parts of Bulgarian Thrace in 1346, 1347, 1349, 1352 and 1354, to which were added the ravages of the Black Death. The Bulgarians' attempts to repel the invaders met with repeated failure, and Ivan Alexander's third son and co-emperor, Ivan Asen IV, was killed in battle against the Turks in 1349, as was his older brother Michael Asen IV in 1355 or a little earlier.

The Black Death (also known as the Pestilence, the Great Mortality or simply, the Plague) was a bubonic plague pandemic occurring in Afro-Eurasia from 1346 to 1353. It is the most fatal pandemic recorded in human history, causing the death of 75–200 million people in Eurasia and North Africa, peaking in Europe from 1347 to 1351. Bubonic plague is caused by the bacterium Yersinia pestis spread by fleas, but it can also take a secondary form where it is spread person-to-person contact via aerosols causing septicaemic or pneumonic plagues.

By 1351 the Byzantine civil war was over, and John VI Kantakouzenos had realized the threat posed by the Ottomans to the Balkan Peninsula. He appealed to the rulers of Serbia and Bulgaria for a united effort against the Turks and asked Ivan Alexander for money to construct warships, but his appeals fell on deaf ears as his neighbours distrusted his intentions. A new attempt for cooperation between Bulgaria and the Byzantine Empire followed in 1355, after John VI Kantakouzenos had been forced to abdicate and John V Palaiologos had been established as supreme emperor. To cement the treaty, Ivan Alexander's daughter Keraca Marija was married off to the future Byzantine Emperor Andronikos IV Palaiologos, but the alliance failed to produce concrete results.

The Savoyard crusade was a crusading expedition to the Balkans in 1366–67. It was born out of the same planning that led to the Alexandrian Crusade and was the brainchild of Pope Urban V. It was led by Count Amadeus VI of Savoy and directed against the growing Ottoman Empire in eastern Europe. Although intended as a collaboration with the Kingdom of Hungary and the Byzantine Empire, the crusade was diverted from its main purpose to attack the Second Bulgarian Empire.

In the wake of the death of Ivan Alexander, the Bulgarian Empire was subdivided into three kingdoms among his sons, with Ivan Shishman taking the Tаrnovo Kingdom situated in central Bulgaria and his half brother Ivan Sratsimir holding the Vidin Tsardom. Although his struggle to repel the Ottomans differentiated him from the other rulers on the Balkans like the Serbian despot Stephan Lazarevic who became a loyal vassal to the Ottomans and paid annual tribute.

Despite the military and political weakness, during his rule Bulgaria remained a major cultural center and the ideas of Hesychasm dominated the Bulgarian Orthodox Church. Ivan Shishman's reign was inextricably connected to the fall of Bulgaria under Ottoman domination.

In 1369, the Ottoman Turks under Murad I conquered Adrianople (in 1363) and made it the effective capital of their expanding state. At the same time, they also captured the Bulgarian cities of Philippopolis and Boruj (Stara Zagora). As Bulgaria and the Serbian princes in Macedonia prepared for united action against the Turks, Ivan Alexander died on 17 February 1371. He was succeeded by his sons Ivan Sracimir in Vidin and Ivan Šišman in Tǎrnovo, while the rulers of Dobruja and Wallachia achieved further independence.

On 26 September 1371, the Ottomans defeated a large Christian army led by the Serbian brothers Vukašin Mrnjavčević and Jovan Uglješa in the Battle of Maritsa. They immediately turned on Bulgaria and conquered northern Thrace, the Rhodopes, Kostenets, Ihtiman, and Samokov, effectively limiting the authority of Ivan Shishman in the lands to the north of the Balkan mountains and the Valley of Sofia. Unable to resist, the Bulgarian monarch was forced to become an Ottoman vassal, and in return he recovered some of the lost towns and secured ten years of uneasy peace.

The Siege of Sofia took place in 1382 or 1385 during the course of the Bulgarian–Ottoman wars. Unable to defend his country from the Ottomans, in 1373 the Bulgarian emperor Ivan Shishman agreed to become an Ottoman vassal and to marry his sister Kera Tamara to their sultan Murad I, while the Ottomans were to return some conquered fortresses. Despite the peace, in the beginning of the 1380s the Ottomans resumed their campaigns and besieged the important city of Sofia which controlled major communication routes to Serbia and Macedonia. There are little records about the siege.

After the futile attempts to storm the city, the Ottoman commander Lala Shahin Pasha considered to abandon the siege. However, a Bulgarian renegate managed to lure the city governor ban Yanuka out of the fortress to hunt and the Turks captured him. Leaderless, the Bulgarians surrendered. The city walls were destroyed and an Ottoman garrison was installed. With the way to the north-west cleared, the Ottomans pressed further and captured Pirot and Niš in 1386, thus wedging between Bulgaria and Serbia.

According to the Anonymous Bulgarian Chronicle, he killed the Wallachian voivode Dan I of Wallachia in September 1386. He also maintained uneasy relations with Ivan Sratsimir, who had broken his last ties with Tarnovo in 1371 and had separated the dioceses of Vidin from the Tarnovo Patriarchate. The two brothers did not cooperate to repel the Ottoman invasion. According to historian Konstantin Jireček, the brothers were engaged in a bitter conflict over Sofia. Ivan Shishman reneged on his vassal obligation to support the Ottomans with troops during their campaigns. Instead, he used every opportunity to participate in Christian coalitions with the Serbs and the Hungarians, provoking massive Ottoman invasions in 1388 and 1393.

After the defeat of the Serbs and Bosniaks in the Battle of Kosovo on 15 June 1389, Ivan Shishman had to seek help from Hungary. During the winter of 1391–1392, he entered into secret negotiations with the King of Hungary Sigismund, who was planning a campaign against the Turks. The new Ottoman sultan Bayezid I pretended to have peaceful intentions in order to cut off Ivan Shishman from his alliance with the Hungarians.

However, in the spring of 1393 Bayezid gathered a large army from his dominions in the Balkans and Asia Minor and attacked Bulgaria. The Ottomans marched to the capital Tarnovo and besieged it. He entrusted the main command to his son Celebi, and ordered him to depart for Tarnovo. Suddenly, the town was besieged from all sides. The Turks threatened the citizens with fire and death if they did not surrender.

The population resisted but eventually surrendered after a three-month siege, following an attack from the direction of Tsarevets, on July 17, 1393. The Patriarch's church "Ascension of Christ" was turned into a mosque, the rest of the churches were also turned into mosques, baths, or stables. All palaces and churches of Trapezitsa were burned down and destroyed. The same fate was expected for the tzar palaces of Tsarevets; however, parts of their walls and towers were left standing until the 17th century.

Ivan Shishman died in 1395 when the Ottomans, led by Bayezid I, took his last fortress Nikopol. In 1396, Ivan Sratsimir joined the Crusade of the Hungarian king Sigismund, but after the Christian army was defeated in the battle of Nicopolis the Ottomans immediately marched on Vidin and seized it, bringing an end to the medieval Bulgarian state.

The Battle of Nicopolis took place on 25 September 1396 and resulted in the rout of an allied crusader army of Hungarian, Croatian, Bulgarian, Wallachian, French, Burgundian, German, and assorted troops (assisted by the Venetian navy) at the hands of an Ottoman force, raising the siege of the Danubian fortress of Nicopolis and leading to the end of the Second Bulgarian Empire. It is often referred to as the Crusade of Nicopolis as it was one of the last large-scale Crusades of the Middle Ages, together with the Crusade of Varna in 1443–1444.