Abu Bakr was the founder and first caliph of the Rashidun Caliphate ruling from 632 until his death in 634. He was the most prominent companion, closest advisor and a father-in-law of the Islamic prophet Muhammad. Abu Bakr is one of the most important figures in Islamic history. Abu Bakr was born in 573 CE to Abu Quhafa and Umm Khayr. He belonged to the tribe of Banu Taym. In the Age of Ignorance, he was a monotheist and condemned idol-worshipping. As a wealthy trader, Abu Bakr used to free slaves. He was an early friend of Muhammad and often used to accompany him on trading in Syria. After Muhammad's invitation of Islam, Abu Bakr became one of the first Muslims. He extensively contributed his wealth in support of Muhammad's work and also accompanied Muhammad, on his migration to Medina.

Soon after Abu Bakr's election, several Arab tribes launched revolts, threatening the unity and stability of the new community and state. These insurgencies and the caliphate's responses to them are collectively referred to as the Ridda Wars ("Wars of Apostasy").

The opposition movements came in two forms, one which challenged the political power of the caliphate, with the other being the acclamation of rival religious ideologies, headed by political leaders who claimed prophethood.

The Ridda Wars, were a series of military campaigns launched by the first caliph Abu Bakr against rebellious Arabian tribes. They began shortly after the death of the Islamic prophet Muhammad in 632 and concluded the next year, with all battles won by the Rashidun Caliphate. These wars secured the caliphate's control over Arabia and restored its nascent prestige.

The Muslim Conquest of Persia, also known as the Arab conquest of Iran, was carried out by the Rashidun Caliphate from 633 to 654 CE and led to the fall of the Sassanid Empire as well as the eventual decline of the Zoroastrian religion. The rise of the Muslims in Arabia coincided with an unprecedented political, social, economic, and military weakness in Persia. Once a major world power, the Sassanid Empire had exhausted its human and material resources after decades of warfare against the Byzantine Empire. The Sassanid state's internal political situation quickly deteriorated after the execution of King Khosrow II in 628. Subsequently, ten new claimants were enthroned within the next four years. Following the Sassanid Civil War of 628–632, the empire was no longer centralized. Arab Muslims first attacked Sassanid territory in 633, when Khalid ibn al-Walid invaded Mesopotamia (then known as the Sassanid province of Asōristān; roughly corresponding to modern-day Iraq), which was the political and economic centre of the Sassanid state. Following the transfer of Khalid to the Byzantine front in the Levant, the Muslims eventually lost their holdings to Sassanid counterattacks. The second Muslim invasion began in 636, under Sa'd ibn Abi Waqqas, when a key victory at the Battle of al-Qadisiyyah led to the permanent end of Sassanid control west of modern-day Iran. For the next six years, the Zagros Mountains, a natural barrier, marked the border between the Rashidun Caliphate and the Sassanid Empire.

Umar ibn al-Khaṭṭāb was the second Rashidun caliph, reigning from 634 until his assassination in 644. He succeeded Abu Bakr (632–634) as the second caliph of the Rashidun Caliphate on 23 August 634. Umar was a senior companion and father-in-law of the Islamic prophet Muhammad. He was also an expert Muslim jurist known for his pious and just nature, which earned him the epithet al-Farooq ("the one who distinguishes (between right and wrong)"). An arbitator of the Adi clan, Umar initially opposed Muhammad, his distant Qurayshid kinsman. After his conversion to Islam in 616, he became the first Muslim to openly pray at the Kaaba. Umar participated in almost all battles and expeditions under Muhammad, who bestowed the title Al-Farooq ('the Distinguisher') upon Umar, for his judgements. After Muhammad's demise, Umar pledged allegiance to Abu Bakr as the first caliph, and served as a close advisor to the latter until his death in 634, when Abu Bakr nominated Umar as his successor. Under Umar, the caliphate expanded at an unprecedented rate, ruling the Sasanian Empire and more than two-thirds of the Byzantine Empire. His attacks against the Sasanian Empire resulted in the conquest of Persia in less than two years (642–644).

The Muslim conquest of the Levant, also known as the Arab conquest of Syria, occurred between 634 and 638 CE. This event was part of the broader Arab-Byzantine Wars. Prior to the conquest, there were clashes between Arabs and Byzantines, notably the Battle of Muʿtah in 629 CE. The conquest began in 634 CE, following the death of Muhammad. It was orchestrated under the leadership of the first two Rashidun caliphs, Abu Bakr and Umar ibn al-Khattab, with Khalid ibn al-Walid playing a crucial role in leading the Rashidun army. This conquest led to the integration of the Levant into the Islamic world as the province of Bilad al-Sham.

The siege of Damascus (634) lasted from 21 August to 19 September 634 before the city fell to the Rashidun Caliphate. Damascus was the first major city of the Eastern Roman Empire to fall in the Muslim conquest of Syria. The last of the Roman–Persian Wars ended in 628, after Heraclius concluded a successful campaign against the Persians in Mesopotamia. At the same time, Muhammad united the Arabs under the banner of Islam. After his death in 632, Abu Bakr succeeded him as the first Rashidun Caliph. Suppressing several internal revolts, Abu Bakr sought to expand the empire beyond the confines of the Arabian Peninsula.

In April 634, Abu Bakr invaded the Byzantine Empire in the Levant and decisively defeated a Byzantine army at the Battle of Ajnadayn. The Muslim armies marched north and laid siege to Damascus. The city was taken after a monophysite bishop informed Khalid ibn al-Walid, the Muslim commander in chief, that it was possible to breach city walls by attacking a position only lightly defended at night. While Khalid entered the city by assault from the Eastern gate, Thomas, commander of the Byzantine garrison, negotiated a peaceful surrender at the Jabiyah gate with Abu Ubaidah, Khalid's second in command. After the surrender of the city, the commanders disputed the terms of the peace agreement.

The Battle of the Yarmuk was a major battle between the army of the Byzantine Empire and the Muslim forces of the Rashidun Caliphate. The battle consisted of a series of engagements that lasted for six days in August 636, near the Yarmouk River, along what are now the borders of Syria–Jordan and Syria–Israel, southeast of the Sea of Galilee.

The result of the battle was a complete Muslim victory that ended Byzantine rule in Syria. The Battle of the Yarmuk is regarded as one of the most decisive battles in military history, and it marked the first great wave of early Muslim conquests after the death of the Islamic prophet Muhammad, heralding the rapid advance of Islam into the then-Christian Levant.

To check the Arab advance and to recover lost territory, Emperor Heraclius had sent a massive expedition to the Levant in May 636. As the Byzantine army approached, the Arabs tactically withdrew from Syria and regrouped all their forces at the Yarmuk plains close to the Arabian Peninsula, where they were reinforced, and defeated the numerically superior Byzantine army. The battle is widely regarded to be Khalid ibn al-Walid's greatest military victory and cemented his reputation as one of the greatest tacticians and cavalry commanders in history.

Caliph 'Umar I started the Muslim calendar counting it from the lunar month, Muharram, in the year of the Prophet's migration to Medina, 16 July in 622 CE.

The Muslim conquest of Egypt, also known as the Rashidun conquest of Egypt, led by the army of 'Amr ibn al-'As, took place between 639 and 646 and was overseen by the Rashidun Caliphate. It ended the seven centuries long period of Roman/Byzantine reign over Egypt that began in 30 BCE. Byzantine rule in the country had been shaken, as Egypt had been conquered and occupied for a decade by the Sassanid Iran in 618–629, before being recovered by the Byzantine emperor Heraclius. The caliphate took advantage of Byzantines' exhaustion and captured Egypt ten years after its reconquest by Heraclius. During the mid-630s, Byzantium had already lost the Levant and its Ghassanid allies in Arabia to the Caliphate. The loss of the prosperous province of Egypt and the defeat of the Byzantine armies severely weakened the empire, resulting in further territorial losses in the centuries to come.

The Battle of Heliopolis or Ayn Shams was a decisive battle between Arab Muslim armies and Byzantine forces for the control of Egypt. Though there were several major skirmishes after this battle, it effectively decided the fate of the Byzantine rule in Egypt, and opened the door for the Muslim conquest of the Byzantine Exarchate of Africa.

Forces of the Rashidun Caliphate seized the major Mediterranean port of Alexandria away from the Byzantine Empire (Eastern Roman Empire) in the middle of the 7th century CE. Alexandria had been the capital of the Byzantine province of Egypt. This ended Eastern Roman maritime control and economic dominance of the Eastern Mediterranean and thus continued to shift geopolitical power further in favor of the Rashidun Caliphate.

The First Battle of Dongola was a battle between early Arab-Muslim forces of the Rashidun Caliphate and the Nubian-Christian forces of the Kingdom of Makuria in 642. The battle, which resulted in a Makurian victory, temporarily halted Arab incursions into Nubia and set the tone for an atmosphere of hostility between the two cultures until the culmination of the Second Battle of Dongola in 652.

In the summer of 642, 'Amr ibn al-'As sent an expedition to the Christian kingdom of Nubia, which bordered Egypt to the south, under the command of his cousin 'Uqbah ibn Nafi as a pre-emptive raid to announce the arrival of new rulers in Egypt. 'Uqbah ibn Nafi, who later made a great name for himself as the conqueror of Africa and led his horse to the Atlantic, had an unhappy experience in Nubia. No pitched battle was fought, but there were only skirmishes and haphazard engagements, the type of warfare in which the Nubians excelled. They were skilful archers and subjected the Muslims to a merciless barrage of arrows, resulting in 250 Muslims losing their eyes in the engagement.

The Nubian cavalry displayed remarkable speed,even more so than the Muslim cavalry. The Nubians would strike hard and then vanish before the Muslims could recover and counterattack. The hit-and-run raids took their toll on the Muslim expedition. 'Uqbah reported that to 'Amr, who ordered 'Uqbah to withdraw from Nubia, terminating the expedition.

On 31 October 644, Abu Lu'lu'a attacked Umar while he was leading the morning prayers, stabbing him six times in the belly and finally in the navel, that proved fatal. Umar was left profusely bleeding while Abu Lu'lu'a tried to flee, but people from all sides rushed to capture him; in his efforts to escape he is reported to have wounded twelve other people, six or nine of whom later died, before slashing himself with his own blade to commit suicide.

Umar's successor, Uthman ibn Affan, was a wealthy Umayyad and early Muslim convert with marital ties to Muhammad. He was elected by the shura council, composed of Muhammad's cousin Ali, al-Zubayr ibn al-Awwam, Talha ibn Ubayd Allah, Sa'd ibn Abi Waqqas and Abd al-Rahman ibn Awf, all of whom were close, early companions of Muhammad and belonged to the Quraysh.He was chosen over Ali because he would ensure the concentration of state power into the hands of the Quraysh, as opposed to Ali's determination to diffuse power among all of the Muslim factions.From early in his reign, Uthman displayed explicit favouritism to his kinsmen, in stark contrast to his predecessors. He appointed his family members as governors over the regions successively conquered under Umar and himself, namely much of the Sasanian Empire, i.e. Iraq and Iran, and the former Byzantine territories of Syria and Egypt.

He ruled for twelve years, the longest of all Rashidun caliphs, and during his reign, the Rashidun Caliphate reached its greatest extent. He is known for having ordered the compilation of the first standard version of the Quran.

The details of the early conquest of Armenia by the Arabs are uncertain, as the various Arabic, Greek, and Armenian sources contradict each other. It was not until 645/646 that a major campaign to subdue Armenia was undertaken by Mu'awiya, the governor of Syria. Mu'awiya's general Habib ibn Maslama al-Fihri first moved against the Byzantine portion of the country: he besieged and captured Theodosiopolis (present-day Erzurum, Turkey) and defeated a Byzantine army, reinforced with Khazar and Alan troops, on the Euphrates. He then turned towards Lake Van, where the local Armenian princes of Akhlat and Moks submitted, allowing Habib to march onto Dvin, the capital of the former Persian portion of Anatolia. Dvin capitulated after a few days of siege, as did Tiflis further north in Caucasian Iberia. During the same time, another Arab army from Iraq, under Salman ibn Rabi'a, conquered parts Caucasian Iberia (Arran).

The Anatolian sources however provide a different narrative, both in chronology and in the details of the events, although the broad thrust of the Arab campaigns is consistent with the Muslim sources.

After the withdrawal of the Byzantines from Egypt, the Exarchate of Africa declared its independence. Under its exarch, Gregory the Patrician, its dominions extended from the borders of Egypt to Morocco. Abdullah ibn Sa'ad sent raiding parties to the west, resulting in considerable booty and encouraging Sa'ad to propose a campaign to conquer the Exarchate.

Uthman gave him permission after considering it in the Majlis al-Shura. A force of 10,000 soldiers was sent as reinforcement. The Rashidun army assembled in Barqa in Cyrenaica, and from there they marched west, captured Tripoli, and then advanced to Sufetula, Gregory's capital. In the Battle of Sufetula, the Exarchate was defeated and Gregory was killed due to the superior tactics of Abdullah ibn Zubayr. Afterward, the people of North Africa sued for peace, agreeing to pay an annual tribute. Instead of annexing North Africa, the Muslims preferred to make North Africa a vassal state. When the stipulated amount of the tribute was paid, the Muslim forces withdrew to Barqa. Following the First Fitna, the first Islamic civil war, Muslim forces withdrew from north Africa to Egypt. The Umayyad Caliphate would later re-invade North Africa in 664.

Muawiya was one of the first to realize the full importance of having a navy; as long as the Byzantine fleet could sail the Mediterranean unopposed, the coastlines of Syria, Palestine and Egypt would never be safe. Muawiyah, along with Abdullah ibn Sa'd, the new governor of Egypt, successfully persuaded Uthman to give them permission to construct a large fleet in the dockyards of Egypt and Syria. Mu'awiyah convinced the caliph a new navy had to be established in order to confront Byzantine naval threat. So he recruited Ubadah ibn al-Samit, along with some veteran companions of Muhammad such as Miqdad Ibn al-Aswad, Abu Dhar GhiFari, Shadaad ibn Aws, Khalid bin Zayd al-Ansari, and Abu Ayyub al-Ansari, participated in building the first Muslim standing Navy in Mediterrania which led by Muawiya. Later Ubadah also joined Abdallah ibn Qais to built the first batch of the ships in Acre.

In 650, Muawiyah attacked Cyprus, conquering the capital, Constantia, after a brief siege, but signed a treaty with the local rulers.

The Second Battle of Dongola or Siege of Dongola was a military engagement between early Arab forces of the Rashidun Caliphate and the Nubian-Christian forces of the kingdom of Makuria in 652. The battle ended Muslim expansion into Nubia, establishing trade and a historic peace between the Muslim world and a Christian nation. As a result, Makuria was able to grow into a regional power that would dominate Nubia for over the next 500 years.

The Battle of the Masts was a crucial naval battle fought in 654 CE between the Muslim Arabs led by Abu al-A'war and the Byzantine fleet under the personal command of Emperor Constans II. The battle is considered to be "the first decisive conflict of Islam on the deep" as well as part of the earliest campaign by Muawiyah to reach Constantinople.

During Umar's reign, the governor of Syria, Muawiyah I, sent a request to build a naval force to invade the islands of the Mediterranean Sea but Umar rejected the proposal because of the risk to the soldiers. Once Uthman became caliph, however, he approved Muawiyah's request. In 650, Muawiyah attacked Cyprus, conquering the capital, Constantia, after a brief siege, but signed a treaty with the local rulers. During this expedition, a relative of Muhammad, Umm-Haram, fell from her mule near the Salt Lake at Larnaca and was killed. She was buried in that same spot, which became a holy site for many local Muslims and Christians and, in 1816, the Hala Sultan Tekke was built there by the Ottomans. After apprehending a breach of the treaty, the Arabs re-invaded the island in 654 with five hundred ships. This time, however, a garrison of 12,000 men was left in Cyprus, bringing the island under Muslim influence. After leaving Cyprus, the Muslim fleet headed towards Crete and then Rhodes and conquered them without much resistance. From 652 to 654, the Muslims launched a naval campaign against Sicily and captured a large part of the island. Soon after this, Uthman was murdered, ending his expansionist policy, and the Muslims accordingly retreated from Sicily. In 655 Byzantine Emperor Constans II led a fleet in person to attack the Muslims at Phoinike (off Lycia) but it was defeated: both sides suffered heavy losses in the battle, and the emperor himself narrowly avoided death.

When Uthman was killed in 656 CE by rebels from Egypt, Kufa and Basra, the potential candidates for caliphate were Alī ibn Abī Ṭālib and Talha. Malik al-Ashtar, the leader of the Kufis, seems to have played a key role in facilitating the caliphate of Ali. The caliphate was offered to Ali and he accepted the position after a few days.

According to Heck, Ali forbade Muslim fighters from looting and instead distributed the taxes as salaries among the warriors, in equal proportions. This might have been the first subject of the dispute between Ali and the group that later constituted the Kharijites. Since the majority of Ali's subjects were nomads and peasants, he was concerned with agriculture. In particular, he instructed his top general, Malik al-Ashtar, to pay more attention to land development than short-term taxation.

The First Fitna was the first Muslim civil war which led to the overthrow of the Rashidun Caliphate and the establishment of the Umayyad Caliphate. The civil war involved three main battles between the fourth Rashidun caliph, Ali, and the rebel groups.

The roots of the first civil war can be traced back to the assassination of the second caliph, Umar. Before he died from his wounds, Umar formed a six-member council, which ultimately elected Uthman as the next caliph. During the final years of Uthman's caliphate, he was accused of nepotism and eventually killed by rebels in 656. After Uthman's assassination, Ali was elected the fourth caliph. Aisha, Talha, and Zubayr revolted against Ali to depose him. The two parties fought the Battle of the Camel in December 656, in which Ali emerged victorious. Afterwards, Mu'awiya, the incumbent governor of Syria, declared war on Ali ostensibly to avenge Uthman's death. The two parties fought the Battle of Siffin in July 657. This battle ended in stalemate and a call for arbitration, which was resented by the Kharijites, who declared Ali, Mu'awiya, and their followers as infidels. Following the Kharijites' violence against civilians, Ali's forces crushed them in the Battle of Nahrawan. Soon after, Mu'awiya also seized control of Egypt with the aid of Amr ibn al-As.

Uthman's nepotism provoked the ire of the Ansar and the members of the shura. In 645/46, he added the Jazira (Upper Mesopotamia) to Mu'awiya's Syrian governorship and granted the latter's request to take possession of all Byzantine crown lands in Syria to help pay his troops. He had the surplus taxes from the wealthy provinces of Kufa and Egypt forwarded to the treasury in Medina, which he used at his personal disposal, frequently disbursing its funds and war booty to his Umayyad relatives. Moreover, the lucrative Sasanian crown lands of Iraq, which Umar had designated as communal property for the benefit of the Arab garrison towns of Kufa and Basra, were turned into caliphal crown lands to be used at Uthman's discretion. Mounting resentment against Uthman's rule in Iraq and Egypt and among the Ansar and Quraysh of Medina culminated in the siege and killing of the caliph in 656.

The Battle of the Camel took place outside of Basra, Iraq, in 656 CE. The battle was fought between the army of the fourth caliph, Ali, on one side, and the rebel army led by Aisha, Talha and Zubayr, on the other side. Ali was the cousin and son-in-law of the Islamic prophet, Muhammad, whereas Aisha was a widow of Muhammad, and Talha and Zubayr were both prominent companions of Muhammad.

The Aisha's party had revolted against Ali ostensibly to avenge the assassination of the third caliph, Uthman. Both the efforts of Ali to save Uthman and the leading roles of Aisha and Talha in inciting Muslims against Uthman are well-cited. Ali emerged victorious from this battle in which Talha and Zubayr were both killed and Aisha was captured.

The Battle of Siffin was fought in 657 CE between Ali ibn Abi Talib, the fourth of the Rashidun Caliphs and the first Shia Imam, and Muawiyah ibn Abi Sufyan, the rebellious governor of Syria. The battle is named after its location, Siffin, on the banks of the Euphrates. The fighting stopped after the Syrians, faced with overwhelming odds of defeat, called for arbitration. The arbitration process ended inconclusively in 658 CE. The battle is considered a part of the First Fitna.

The Battle of Nahrawan was fought between the army of Caliph Ali and the rebel group Kharijites in July 658 CE. They were a group of pious allies of Ali during the First Muslim Civil War. They separated from him following the Battle of Siffin when Ali agreed to settle the dispute with Mu'awiya, governor of Syria, through negotiations, a move labeled by the group as against the Qur'an. After failed attempts to regain their loyalty and because of their rebellious and murderous activities, Ali confronted the Kharijites near their headquarters by the Nahrawan Canal, near modern-day Baghdad. Of the 4,000 rebels, some 1,200 were won over with the promise of amnesty while the majority of the remaining 2,800 rebels were killed in the ensuing battle. Other sources put the casualties at 1500–1800. The battle resulted in a permanent split between the group and the rest of the Muslims, whom the Kharijites branded as apostates. Although defeated, they continued to threaten and harass cities and towns for several years. Ali was assassinated by a Kharijite in January 661.

In 661, on the nineteenth of Ramadan, while Ali was praying in the Great Mosque of Kufa, he was struck over the head with a poison-coated sword by the Kharijite Abd al-Rahman ibn Muljam. Ali died two days later from his wound. The sources seem to be unanimous that Ali forbade his family from excessive punishments for Ibn Muljam and from shedding the blood of others. In the meantime, Ibn Muljam was to be given good meals and a good bed. After Ali's death, his eldest son, Hasan, observed the lex talionis and Ibn Muljam was executed. Ali's grave was kept secret out of the fear that it might be desecrated by his enemies.

Key Findings:

• The Rashidun Caliphate is characterized by a twenty-five-year period of rapid;military expansion;followed by a five-year period of;internal strife.
• The caliphate had subjugated the Levant to the Transcaucasus in the north; North Africa from Egypt to present-day Tunisia in the west; and the Iranian Plateau to parts of Central Asia and South Asia in the east.;
• The Rashidun were also;responsible for the adoption of an Islamic calendar.
• The judicial administration, like the rest of the administrative structure of the Rashidun Caliphate, was set up by Umar, and it remained basically unchanged throughout the duration of the Caliphate.
• Social welfare and pensions were introduced in early Islamic law as forms of zakāt (charity), one of the Five Pillars of Islam, since the time of Umar.
• After consulting the Companions, Umar decided to establish the Bait-ul-Maal (central Treasury) at Medina.
• During the caliphate of Umar, many new cities were founded. These included Kufa, Basra, and Fustat.
• The Rashidun were also responsible for the establishment of an;authoritative;reading of the;Qurʾān, which strengthened the Muslim community and encouraged religious scholarship.;