Pre-Celtic tribes inhabited Portugal leaving a remarkable cultural footprint. The Cynetes developed a written language, leaving many stelae, which are mainly found in the south of Portugal. Early in the first millennium BCE, several waves of Celts invaded Portugal from Central Europe and intermarried with the local populations to form several different ethnic groups, with many tribes. The Celtic presence in Portugal is traceable, in broad outline, through archaeological and linguistic evidence. They dominated much of northern and central Portugal; but in the south, they were unable to establish their stronghold, which retained its non-Indo-European character until the Roman conquest. In southern Portugal, some small, semi-permanent commercial coastal settlements were also founded by Phoenician-Carthaginians.

Romanization began with the arrival of the Roman army in the Iberian Peninsula in 218 BCE during the Second Punic War against Carthage. The Romans sought to conquer Lusitania, a territory that included all of modern Portugal south of the Douro river and Spanish Extremadura, with its capital at Emerita Augusta (now Mérida).

Mining was the primary factor that made the Romans interested in conquering the region: one of Rome's strategic objectives was to cut off Carthaginian access to the Iberian copper, tin, gold, and silver mines. The Romans intensely exploited the Aljustrel (Vipasca) and Santo Domingo mines in the Iberian Pyrite Belt which extends to Seville.

Shows Iberian peninsula in 125 including important roads, legionnaire locations and gold/silver mines. © ArdadN

While the south of what is now Portugal was relatively easily occupied by the Romans, the conquest of the north was achieved only with difficulty due to resistance from Serra da Estrela by Celts and Lusitanians led by Viriatus, who managed to resist Roman expansion for years. Viriatus, a shepherd from Serra da Estrela who was expert in guerrilla tactics, waged relentless war against the Romans, defeating several successive Roman generals, until he was assassinated in 140 BCE by traitors bought by the Romans. Viriatus has long been hailed as the first truly heroic figure in proto-Portuguese history. Nonetheless, he was responsible for raids into the more settled Romanized parts of Southern Portugal and Lusitania that involved the victimization of the inhabitants.

The conquest of the Iberian Peninsula was complete two centuries after the Roman arrival, when they defeated the remaining Cantabri, Astures and Gallaeci in the Cantabrian Wars in the time of Emperor Augustus (19 BCE). In 74 CE, Vespasian granted Latin Rights to most municipalities of Lusitania. In 212 CE, the Constitutio Antoniniana gave Roman citizenship to all free subjects of the empire and, at the end of the century, the emperor Diocletian founded the province of Gallaecia, which included modern-day northern Portugal, with its capital at Bracara Augusta (now Braga). As well as mining, the Romans also developed agriculture, on some of the best agricultural land in the empire. In what is now Alentejo, vines and cereals were cultivated, and fishing was intensively pursued in the coastal belt of the Algarve, Póvoa de Varzim, Matosinhos, Troia and the coast of Lisbon, for the manufacture of garum that was exported by Roman trade routes to the entire empire. Business transactions were facilitated by coinage and the construction of an extensive road network, bridges and aqueducts, such as Trajan's bridge in Aquae Flaviae (now Chaves).

In 409, with the decline of the Roman Empire, the Iberian Peninsula was occupied by Germanic tribes that the Romans referred to as barbarians. In 411, with a federation contract with Emperor Honorius, many of these people settled in Hispania. An important group was made up of the Suebi and Vandals in Gallaecia, who founded a Suebi Kingdom with its capital in Braga. They came to dominate Aeminium (Coimbra) as well, and there were Visigoths to the south. The Suebi and the Visigoths were the Germanic tribes who had the most lasting presence in the territories corresponding to modern Portugal. As elsewhere in Western Europe, there was a sharp decline in urban life during the Dark Ages.

Roman institutions disappeared in the wake of the Germanic invasions with the exception of ecclesiastical organizations, which were fostered by the Suebi in the fifth century and adopted by the Visigoths afterwards. Although the Suebi and Visigoths were initially followers of Arianism and Priscillianism, they adopted Catholicism from the local inhabitants. St. Martin of Braga was a particularly influential evangelist at this time.

A map showing the movements of Suebi across Europe. © Theutatis

In 429, the Visigoths moved south to expel the Alans and Vandals and founded a kingdom with its capital in Toledo. From 470, conflict between the Suebi and Visigoths increased. In 585, the Visigothic King Liuvigild conquered Braga and annexed Gallaecia. From that time, the Iberian Peninsula was unified under a Visigothic Kingdom.

The Umayyad conquest of Hispania, also known as the Umayyad conquest of the Visigothic Kingdom, was the initial expansion of the Umayyad Caliphate over Hispania (in the Iberian Peninsula) from 711 to 718. The conquest resulted in the destruction of the Visigothic Kingdom and the establishment of the Umayyad Wilayah of Al-Andalus. During the caliphate of the sixth Umayyad caliph al-Walid I (r. 705–715), forces led by Tariq ibn Ziyad disembarked in early 711 in Gibraltar at the head of an army consisting of Berbers from north Africa. After defeating the Visigothic king Roderic at the decisive Battle of Guadalete, Tariq was reinforced by an Arab force led by his superior wali Musa ibn Nusayr and continued northward. By 717, the combined Arab-Berber force had crossed the Pyrenees into Septimania. They occupied further territory in Gaul until 759.

Umayyad conquest of Hispania map. © ICL

The Reconquista is a historiographical construction of the 781-year period in the history of the Iberian Peninsula between the Umayyad conquest of Hispania in 711 and the fall of the Nasrid kingdom of Granada in 1492, in which the Christian kingdoms expanded through war and conquered al-Andalus, or the territories of Iberia ruled by Muslims.

The beginning of the Reconquista is traditionally marked with the Battle of Covadonga (718 or 722), the first known victory by Christian military forces in Hispania since the 711 military invasion which was undertaken by combined Arab-Berber forces. The rebels who were led by Pelagius defeated a Muslim army in the mountains of northern Hispania and established the independent Christian Kingdom of Asturias.

In the late 10th century, the Umayyad vizier Almanzor waged military campaigns for 30 years to subjugate the northern Christian kingdoms. His armies ravaged the north, even sacking the great Santiago de Compostela Cathedral. When the government of Córdoba disintegrated in the early 11th century, a series of petty successor states known as taifas emerged. The northern kingdoms took advantage of this situation and struck deep into al-Andalus; they fostered civil war, intimidated the weakened taifas, and made them pay large tributes (parias) for "protection".

After a Muslim resurgence under the Almohads in the 12th century, the great Moorish strongholds in the south fell to Christian forces in the 13th century after the decisive battle of Las Navas de Tolosa (1212)—Córdoba in 1236 and Seville in 1248—leaving only the Muslim enclave of Granada as a tributary state in the south. After the surrender of Granada in January 1492, the entire Iberian peninsula was controlled by Christian rulers. On 30 July 1492, as a result of the Alhambra Decree, all the Jewish community—some 200,000 people—were forcibly expelled. The conquest was followed by a series of edicts (1499–1526) which forced the conversions of Muslims in Spain, who were later expelled from the Iberian peninsula by the decrees of King Philip III in 1609.

The history of the county of Portugal is traditionally dated from the reconquest of Portus Cale (Porto) by Vímara Peres in 868. He was named a count and given control of the frontier region between the Limia and Douro rivers by Alfonso III of Asturias. South of the Douro, another border county would be formed decades later when what would become the County of Coimbra was conquered from the Moors by Hermenegildo Guterres. This moved the frontier away from the southern bounds of the county of Portugal, but it was still subject to repeated campaigns from the Caliphate of Córdoba. The recapture of Coimbra by Almanzor in 987 again placed the County of Portugal on the southern frontier of the Leonese state for most of the rest of the first county's existence. The regions to its south were only again conquered in the reign of Ferdinand I of León and Castile, with Lamego falling in 1057, Viseu in 1058 and finally Coimbra in 1064.

The county continued with varying degrees of autonomy within the Kingdom of León and, during brief periods of division, the Kingdom of Galicia until 1071, when Count Nuno Mendes, desiring greater autonomy for Portugal, was defeated and killed in the Battle of Pedroso by King García II of Galicia, who then proclaimed himself the King of Galicia and Portugal, the first time a royal title was used in reference to Portugal. The independent county was abolished, its territories remaining within the crown of Galicia, which was in turn subsumed within the larger kingdoms of García's brothers, Sancho II and Alfonso VI of León and Castile.

In 1093, Alfonso VI nominated his son-in-law Raymond of Burgundy as count of Galicia, then including modern Portugal as far south as Coimbra, though Alfonso himself retained the title of king over the same territory. However, concern for Raymond's growing power led Alfonso in 1096 to separate Portugal and Coimbra from Galicia and grant them to another son-in-law, Henry of Burgundy, wed to Alfonso VI's illegitimate daughter Theresa. Henry chose Guimarães as the base for this newly formed county, the Condado Portucalense, known at the time as Terra Portucalense or Província Portucalense, which would last until Portugal achieved its independence, recognized by the Kingdom of León in 1143. Its territory included much of the current Portuguese territory between the Minho River and the Tagus River.

At the end of the 11th century, the Burgundian knight Henry became count of Portugal and defended its independence by merging the County of Portugal and the County of Coimbra. His efforts were assisted by a civil war that raged between León and Castile and distracted his enemies. Henry's son Afonso Henriques took control of the county upon his death. The city of Braga, the unofficial Catholic centre of the Iberian Peninsula, faced new competition from other regions. Lords of the cities of Coimbra and Porto fought with Braga's clergy and demanded the independence of the reconstituted county.

The Battle of São Mamede took place on 24 June 1128 near Guimarães and is considered the seminal event for the foundation of the Kingdom of Portugal and the battle that ensured Portugal's Independence. Portuguese forces led by Afonso Henriques defeated forces led by his mother Teresa of Portugal and her lover Fernão Peres de Trava. Following São Mamede, the future king styled himself "Prince of Portugal". He would be called "King of Portugal" starting in 1139 and was recognised as such by neighbouring kingdoms in 1143.

The Battle of Ourique was a battle that took place on 25 July 1139, in which the forces of Portuguese count Afonso Henriques (of the House of Burgundy) defeated those led by the Almoravid governor of Córdoba, Muhammad Az-Zubayr Ibn Umar, identified as "King Ismar" in Christian chronicles.

Shortly after the battle, Afonso Henriques is said to have called for the first assembly of the estates-general of Portugal at Lamego, where he was given the crown from the Primate Archbishop of Braga, to confirm the Portuguese independence from the Kingdom of León. This was a patriotic falsification perpetuated by the clergy, nobility, and supporters who promoted the restoration of Portuguese sovereignty and the claims of John IV, after the Iberian Union. The documents that refer to the estates-general were "deciphered" by Cistercian monks from the Monastery of Alcobaça to perpetuate the myth and justify the legitimacy of the Portuguese crown in the 17th century.

The siege of Lisbon, from 1 July to 25 October 1147, was the military action that brought the city of Lisbon under definitive Portuguese control and expelled its Moorish overlords. The siege of Lisbon was one of the few Christian victories of the Second Crusade—it was "the only success of the universal operation undertaken by the pilgrim army", i.e., the Second Crusade, according to the near contemporary historian Helmold, though others have questioned whether it was really part of that crusade. It is seen as a pivotal battle of the wider Reconquista.

The crusaders agreed to help the King attack Lisbon, with a solemn agreement that offered to the crusaders the pillage of the city's goods and the ransom money for expected prisoners. The siege began on 1 July. The city of Lisbon at the time of arrival consisted of sixty thousand families, including the refugees who had fled Christian onslaught from neighbouring cities of Santarém and others.

After four months, the Moorish rulers agreed to surrender on 24 October, primarily because of hunger within the city. Most of the crusaders settled in the newly captured city, but some of the crusaders set sail and continued to the Holy Land. Lisbon eventually became the capital city of the Kingdom of Portugal, in 1255.

The Algarve, the southernmost region of Portugal, was finally conquered from the Moors in 1249, and in 1255 the capital shifted to Lisbon. Neighboring Spain would not complete its Reconquista until 1492, almost 250 years later. Portugal's land boundaries have been notably stable for the rest of the country's history. The border with Spain has remained almost unchanged since the 13th century.

The 1383–1385 Portuguese interregnum was a civil war in Portuguese history during which no crowned king of Portugal reigned. The interregnum began when King Ferdinand I died without a male heir and ended when King John I was crowned in 1385 after his victory during the Battle of Aljubarrota.

The Portuguese interpret the era as their earliest national resistance movement to counter Castilian intervention, and Robert Durand considers it as the "great revealer of national consciousness". The bourgeoisie and the nobility worked together to establish the Aviz dynasty, a branch of the Portuguese House of Burgundy, securely on an independent throne. That contrasted with the lengthy civil wars in France (Hundred Years' War) and England (War of the Roses), which had aristocratic factions fighting powerfully against a centralised monarchy. It is usually known in Portugal as the 1383–1385 Crisis (Crise de 1383–1385).

The Battle of Aljubarrota was fought between the Kingdom of Portugal and the Crown of Castile on 14 August 1385. Forces commanded by King John I of Portugal and his general Nuno Álvares Pereira, with the support of English allies, opposed the army of King John I of Castile with its Aragonese, Italian and French allies at São Jorge, between the towns of Leiria and Alcobaça, in central Portugal. The result was a decisive victory for the Portuguese, ruling out Castilian ambitions to the Portuguese throne, ending the 1383–85 Crisis and assuring John as King of Portugal. Portuguese independence was confirmed and a new dynasty, the House of Aviz, was established. Scattered border confrontations with Castilian troops would persist until the death of John I of Castile in 1390, but these posed no real threat to the new dynasty.

The Treaty of Windsor is the diplomatic alliance signed between Portugal and England on 9 May 1386 at Windsor and sealed by the marriage of King John I of Portugal (House of Aviz) to Philippa of Lancaster, daughter of John of Gaunt, 1st Duke of Lancaster. With the victory at the Battle of Aljubarrota, assisted by English archers, John I was recognised as the undisputed King of Portugal, putting an end to the interregnum of the 1383–1385 Crisis. The Treaty of Windsor established a pact of mutual support between the countries. The treaty created an alliance between Portugal and England that remains in effect to this day.

In the early 1400s, Portugal cast an eye at gaining Ceuta. The prospect of taking of Ceuta offered the younger nobility an opportunity to win wealth and glory. The chief promoter of the Ceuta expedition was João Afonso, royal overseer of finance. Ceuta's position opposite the straits of Gibraltar gave it control of one of the main outlets of the trans-African Sudanese gold trade; and it could enable Portugal to flank its most dangerous rival, Castile.

On the morning of 21 August 1415, John I of Portugal led his sons and their assembled forces in a surprise assault on Ceuta, landing on Playa San Amaro. The battle itself was almost anticlimactic, because the 45,000 men who traveled on 200 Portuguese ships caught the defenders of Ceuta off guard. By nightfall the town was captured.

Possession of Ceuta would indirectly lead to further Portuguese expansion. The main area of Portuguese expansion, at this time, was the coast of Morocco, where there was grain, cattle, sugar, and textiles, as well as fish, hides, wax, and honey. Ceuta had to endure alone for 43 years, until the position of the city was consolidated with the taking of Ksar es-Seghir (1458), Arzila and Tangier (1471). The city was recognized as a Portuguese possession by the Treaty of Alcáçovas (1479) and by the Treaty of Tordesilhas (1494).

In 1415, the Portuguese occupied the North African city of Ceuta, aiming to gain a foothold on Morocco, to control navigation through the Strait of Gibraltar, expand Christianity with the backing of the Pope, and by pressure of the nobility for epic and profitable acts of war, now that Portugal had finished the Reconquista on the Iberian Peninsula. Among the participants of the action was the young Prince Henry the Navigator. Appointed governor of the Order of Christ in 1420, while personally holding profitable monopolies on resources in Algarve, he took the lead role in encouraging Portuguese maritime exploration until his death in 1460. He invested in sponsoring voyages down the coast of Mauritania, gathering a group of merchants, shipowners, stakeholders and participants interested in the sea lanes. Later his brother Prince Pedro granted him a royal monopoly of all profits from trading within the areas discovered.

In 1418, two of Henry's captains, João Gonçalves Zarco and Tristão Vaz Teixeira were driven by a storm to Porto Santo an uninhabited island off the coast of Africa which may have been known to Europeans since the 14th century. In 1419 Zarco and Teixeira made a landfall on Madeira. They returned with Bartolomeu Perestrelo and Portuguese settlement of the islands began. There, wheat and later sugarcane were cultivated, as in Algarve, by the Genoese, becoming profitable activities. This helped both them and Prince Henry become wealthier.

In 1434, Gil Eanes passed Cape Bojador, south of Morocco. The trip marked the beginning of the Portuguese exploration of Africa. Before this event, very little was known in Europe about what lay beyond the cape. At the end of the 13th century and the beginning of the 14th, those who tried to venture there became lost, which gave birth to legends of sea monsters. Some setbacks occurred: in 1436 the Canaries were officially recognized as Castilian by the pope—earlier they had been recognized as Portuguese; in 1438, the Portuguese were defeated in a military expedition to Tangier.

During the territorial and economic expansion of the Age of Discovery, the factory was adapted by the Portuguese and spread throughout from West Africa to Southeast Asia. The Portuguese feitorias were mostly fortified trading posts settled in coastal areas, built to centralize and thus dominate the local trade of products with the Portuguese kingdom (and thence to Europe). They served simultaneously as market, warehouse, support to the navigation and customs and were governed by a feitor ("factor") responsible for managing the trade, buying and trading products on behalf of the king and collecting taxes (usually 20%).

The first Portuguese feitoria overseas was established by Henry the Navigator in 1445 on the island of Arguin, off the coast of Mauritania. It was built to attract Muslim traders and monopolize the business in the routes traveled in North Africa. It served as a model for a chain of African feitorias, Elmina Castle being the most notorious.

Between the 15th and 16th centuries, a chain of about 50 Portuguese forts either housed or protected feitorias along the coasts of West and East Africa, the Indian Ocean, China, Japan, and South America. The main factories of the Portuguese East Indies, were in Goa, Malacca, Ormuz, Ternate, Macao, and the richest possession of Bassein that went on become the financial centre of India as Bombay (Mumbai). They were mainly driven by the trade of gold and slaves on the coast of Guinea, spices in the Indian Ocean, and sugar cane in the New World. They were also used for local triangular trade between several territories, like Goa-Macau-Nagasaki, trading products such as sugar, pepper, coconut, timber, horses, grain, feathers from exotic Indonesian birds, precious stones, silks and porcelain from the East, among many other products. In the Indian Ocean, the trade in Portuguese factories was enforced and increased by a merchant ship licensing system: the cartazes.

From the feitorias, the products went to the main outpost in Goa, then to Portugal where they were traded in the Casa da Índia, which also managed exports to India. There they were sold, or re-exported to the Royal Portuguese Factory in Antwerp, where they were distributed to the rest of Europe.

Easily supplied and defended by sea, the factories worked as independent colonial bases. They provided safety, both for the Portuguese, and at times for the territories in which they were built, protecting against constant rivalries and piracy. They allowed Portugal to dominate trade in the Atlantic and Indian oceans, establishing a vast empire with scarce human and territorial resources. Over time, the feitorias were sometimes licensed to private entrepreneurs, giving rise to some conflict between abusive private interests and local populations, such as in the Maldives.

In the 1470s, Portuguese trading ships reached the Gold Coast. In 1471, the Portuguese captured Tangier, after years of attempts. Eleven years later, the fortress of São Jorge da Mina in the town of Elmina on the Gold Coast in the Gulf of Guinea was built. 

In 1488, Bartolomeu Dias became the first European navigator to round the southern tip of Africa and to demonstrate that the most effective southward route for ships lay in the open ocean, well to the west of the African coast. His discoveries effectively established the sea route between Europe and Asia.

The Treaty of Tordesillas, signed in Tordesillas, Spain on 7 June 1494, and authenticated in Setúbal, Portugal, divided the newly discovered lands outside Europe between the Portuguese Empire and the Spanish Empire (Crown of Castile), along a meridian 370 leagues west of the Cape Verde islands, off the west coast of Africa. That line of demarcation was about halfway between the Cape Verde islands (already Portuguese) and the islands entered by Christopher Columbus on his first voyage (claimed for Castile and León), named in the treaty as Cipangu and Antillia (Cuba and Hispaniola).

The lands to the east would belong to Portugal and the lands to the west to Castile, modifying an earlier division proposed by Pope Alexander VI. The treaty was signed by Spain, 2 July 1494, and by Portugal, 5 September 1494. The other side of the world was divided a few decades later by the Treaty of Zaragoza, signed on 22 April 1529, which specified the antimeridian to the line of demarcation specified in the Treaty of Tordesillas. Originals of both treaties are kept at the General Archive of the Indies in Spain and at the Torre do Tombo National Archive in Portugal.

Despite considerable lack of information regarding the geography of the New World, Portugal and Spain largely respected the treaty. The other European powers however did not sign the treaty and generally ignored it, particularly those that became Protestant after the Reformation.

The Portuguese discovery of the sea route to India was the first recorded trip directly from Europe to the Indian subcontinent, via the Cape of Good Hope. Under the command of Portuguese explorer Vasco da Gama, it was undertaken during the reign of King Manuel I in 1495–1499. Considered one of the most remarkable voyages of the Age of Discovery, it initiated the Portuguese maritime trade at Fort Cochin and other parts of the Indian Ocean, the military presence and settlements of the Portuguese in Goa and Bombay.

In April 1500, the second Portuguese India Armada, headed by Pedro Álvares Cabral, with a crew of expert captains, including Bartolomeu Dias and Nicolau Coelho, encountered the Brazilian coast as it swung westward in the Atlantic while performing a large "volta do mar" to avoid becalming in the Gulf of Guinea. On 21 April 1500, a mountain was seen that was named Monte Pascoal, and on 22 April, Cabral landed on the coast, in Porto Seguro. Believing the land to be an island, he named it Ilha de Vera Cruz (Island of the True Cross). The previous expedition of Vasco da Gama to India already recorded several signs of land near its western open Atlantic Ocean route, in 1497. It has also been suggested that Duarte Pacheco Pereira may have discovered the coasts of Brazil in 1498, possible its northeast, but the exact area of the expedition and the explored regions remain unclear. On the other hand, some historians have suggested that the Portuguese may have encountered the South American bulge earlier while sailing the "volta do mar" (in the Southwest Atlantic), hence the insistence of King John II in moving the line west of the line agreed upon in the Treaty of Tordesillas in 1494. From the east coast, the fleet then turned eastward to resume the journey to the southern tip of Africa and India. Landing in the New World and reaching Asia, the expedition connected four continents for the first time in history.

The Battle of Diu was a naval battle fought on 3 February 1509 in the Arabian Sea, in the port of Diu, India, between the Portuguese Empire and a joint fleet of the Sultan of Gujarat, the Mamlûk Burji Sultanate of Egypt, and the Zamorin of Calicut with support of the Republic of Venice and the Ottoman Empire.

The Portuguese victory was critical: the great Muslim alliance was soundly defeated, easing the Portuguese strategy of controlling the Indian Ocean to route trade down the Cape of Good Hope, circumventing the historical spice trade controlled by the Arabs and the Venetians through the Red Sea and Persian Gulf. After the battle, Kingdom of Portugal rapidly captured several key ports in the Indian Ocean including Goa, Ceylon, Malacca, Bom Baim and Ormuz. The territorial losses crippled the Mamluk Sultanate and the Gujarat Sultanate. The battle catalpulted the growth of the Portuguese Empire and established its political dominance for more than a century. Portuguese power in the East would begin to decline with the sackings of Goa and Bombay-Bassein, Portuguese Restoration War and the Dutch colonisation of Ceylon.

The Battle of Diu was a battle of annihilation similar to the Battle of Lepanto and the Battle of Trafalgar, and one of the most important in world naval history, for it marks the beginning of European dominance over Asian seas that would last until the Second World War.

The Portuguese conquest of Goa occurred when the governor Afonso de Albuquerque captured the city in 1510 from the Adil Shahis. Goa, which became the capital of the Portuguese East Indies and Portuguese Indian territories such as Bom Baim, was not among the places Albuquerque was supposed to conquer. He did so after he was offered the support and guidance of Timoji and his troops. Albuquerque had been given orders by Manuel I of Portugal to capture Hormuz, Aden and Malacca only.

The Capture of Malacca in 1511 occurred when the governor of Portuguese India Afonso de Albuquerque conquered the city of Malacca in 1511. The port city of Malacca controlled the narrow, strategic Strait of Malacca, through which all seagoing trade between China and India was concentrated. The capture of Malacca was the result of a plan by King Manuel I of Portugal, who since 1505 had intended to beat the Castilians to the Far-East, and Albuquerque's own project of establishing firm foundations for Portuguese India, alongside Hormuz, Goa and Aden, to ultimately control trade and thwart Muslim shipping in the Indian Ocean.Having started sailing from Cochin in April 1511, the expedition would not have been able to turn around due to contrary monsoon winds. Had the enterprise failed, the Portuguese could not hope for reinforcements and would have been unable to return to their bases in India. It was the farthest territorial conquest in the history of mankind until then.

The Ottoman-Portuguese conflicts (1538 to 1559) were a series of armed military encounters between the Portuguese Empire and the Ottoman Empire along with regional allies in and along the Indian Ocean, Persian Gulf, and Red Sea. This is a period of conflict during the Ottoman–Portuguese confrontations.

In 1542 Jesuit missionary Francis Xavier arrived in Goa at the service of King John III of Portugal, in charge of an Apostolic Nunciature. At the same time Francisco Zeimoto, António Mota, and other traders arrived in Japan for the first time. According to Fernão Mendes Pinto, who claimed to be in this journey, they arrived at Tanegashima, where the locals were impressed by European firearms, which would be immediately made by the Japanese on a large scale. In 1557 the Chinese authorities allowed the Portuguese to settle in Macau through an annual payment, creating a warehouse in the triangular trade between China, Japan and Europe. In 1570 the Portuguese bought a Japanese port where they founded the city of Nagasaki, thus creating a trading center that for many years was the port from Japan to the world.

The Iberian Union refers to the dynastic union of the Kingdoms of Castile and Aragon and the Kingdom of Portugal under the Castilian Crown that existed between 1580 and 1640 and brought the entire Iberian Peninsula, as well as Portuguese overseas possessions, under the Spanish Habsburg Kings Philip II, Philip III and Philip IV. The union began after the Portuguese crisis of succession and the ensuing War of the Portuguese Succession, and lasted until the Portuguese Restoration War during which the House of Braganza was established as Portugal's new ruling dynasty.

The Habsburg king, the only element that connected the multiple kingdoms and territories, ruled by the six separate government councils of Castile, Aragon, Portugal, Italy, Flanders and the Indies. The governments, institutions and legal traditions of each kingdom remained independent of one another. Alien laws (Leyes de extranjería) determined that a national of one kingdom was a foreigner in all other kingdoms.

The War of the Portuguese Succession, a result of the extinction of the Portuguese royal line after the Battle of Alcácer Quibir and the ensuing Portuguese succession crisis of 1580, was fought from 1580 to 1583 between the two main claimants to the Portuguese throne: António, Prior of Crato, proclaimed in several towns as King of Portugal, and his first cousin Philip II of Spain, who eventually succeeded in claiming the crown, reigning as Philip I of Portugal.

The Portuguese Restoration War was the war between Portugal and Spain that began with the Portuguese revolution of 1640 and ended with the Treaty of Lisbon in 1668, bringing a formal end to the Iberian Union. The period from 1640 to 1668 was marked by periodic skirmishes between Portugal and Spain, as well as short episodes of more serious warfare, much of it occasioned by Spanish and Portuguese entanglements with non-Iberian powers. Spain was involved in the Thirty Years' War until 1648 and the Franco-Spanish War until 1659, while Portugal was involved in the Dutch–Portuguese War until 1663. In the seventeenth century and afterwards, this period of sporadic conflict was simply known, in Portugal and elsewhere, as the Acclamation War. The war established the House of Braganza as Portugal's new ruling dynasty, replacing the House of Habsburg who had been united with the Portuguese crown since the 1581 succession crisis.

In 1693, gold was discovered at Minas Gerais in Brazil. Major discoveries of gold and, later, diamonds in Minas Gerais, Mato Grosso and Goiás led to a "gold rush", with a large influx of migrants. The village became the new economic center of the empire, with rapid settlement and some conflicts. This gold cycle led to the creation of an internal market and attracted a large number of immigrants.

The gold rush considerably increased the revenue of the Portuguese crown, who charged a fifth of all the ore mined, or the "fifth". Diversion and smuggling were frequent, along with altercations between Paulistas (residents of São Paulo) and Emboabas (immigrants from Portugal and other regions in Brazil), so a whole set of bureaucratic controls began in 1710 with the captaincy of São Paulo and Minas Gerais. By 1718, São Paulo and Minas Gerais became two captaincies, with eight vilas created in the latter. The crown also restricted the diamond mining within its jurisdiction and to private contractors. In spite of gold galvanizing global trade, the plantation industry became the leading export for Brazil during this period; sugar constituted at 50% of the exports (with gold at 46%) in 1760.

Gold discovered in Mato Grosso and Goiás sparked an interest to solidify the western borders of the colony. In the 1730s contact with Spanish outposts occurred more frequently, and the Spanish threatened to launch a military expedition in order to remove them. This failed to happen and by the 1750s the Portuguese were able to implant a political stronghold in the region.

The 1755 Lisbon earthquake, also known as the Great Lisbon earthquake, impacted Portugal, the Iberian Peninsula, and Northwest Africa on the morning of Saturday, 1 November, Feast of All Saints, at around 09:40 local time. In combination with subsequent fires and a tsunami, the earthquake almost completely destroyed Lisbon and adjoining areas. Seismologists estimate the Lisbon earthquake had a magnitude of 7.7 or greater on the moment magnitude scale, with its epicenter in the Atlantic Ocean about 200 km (120 mi) west-southwest of Cape St. Vincent and about 290 km (180 mi) southwest of Lisbon.

Chronologically, it was the third known large scale earthquake to hit the city (following those of 1321 and 1531). Estimates place the death toll in Lisbon at between 12,000 and 50,000 people, making it one of the deadliest earthquakes in history.

The earthquake accentuated political tensions in Portugal and profoundly disrupted the country's colonial ambitions. The event was widely discussed and dwelt upon by European Enlightenment philosophers, and inspired major developments in theodicy. As the first earthquake studied scientifically for its effects over a large area, it led to the birth of modern seismology and earthquake engineering.

Pombal secured his preeminence through his decisive management of the 1755 Lisbon earthquake, one of the deadliest earthquakes in history; he maintained public order, organized relief efforts, and supervised the capital's reconstruction in the Pombaline architectural style. Pombal was appointed as Secretary of State for Internal Affairs in 1757 and consolidated his authority during the Távora affair of 1759, which resulted in the execution of leading members of the aristocratic party and allowed Pombal to suppress the Society of Jesus. In 1759, Joseph granted Pombal the title of Count of Oeiras and, in 1769, that of Marquis of Pombal.

A leading estrangeirado strongly influenced by his observations of British commercial and domestic policy, Pombal implemented sweeping commercial reforms, establishing a system of companies and guilds governing each industry. These efforts included the demarcation of the Douro wine region, created to regulate the production and trade of port wine. In foreign policy, although Pombal desired to decrease Portuguese reliance on Great Britain, he maintained the Anglo-Portuguese Alliance, which successfully defended Portugal from Spanish invasion during the Seven Years' War. He expelled the Jesuits in 1759, created the basis for secular public primary and secondary schools, introduced vocational training, created hundreds of new teaching posts, added departments of mathematics and natural sciences to the University of Coimbra, and introduced new taxes to pay for these reforms. Pombal enacted liberal domestic policies, including the prohibition of the import of black slaves within Portugal and Portuguese India, and greatly weakened the Portuguese Inquisition, and granting civil rights to the New Christians. Despite these reforms, Pombal governed autocratically, curtailing individual liberties, suppressing political opposition, and fostered the slave trade to Brazil. Following the accession of Queen Maria I in 1777, Pombal was stripped of his offices and ultimately exiled to his estates, where he died in 1782.

The Spanish invasion of Portugal between 5 May and 24 November 1762 was a military episode in the wider Seven Years' War in which Spain and France were defeated by the Anglo-Portuguese Alliance with broad popular resistance. It involved at first the forces of Spain and Portugal until France and Great Britain intervened in the conflict on the side of their respective allies. The war was also strongly marked by guerrilla warfare in the mountainous country, which cut off supplies from Spain, and a hostile peasantry, which enforced a scorched earth policy as the invading armies approached that left the invaders starving and short of military supplies and forced them to retreat with heavy losses, mostly from starvation, disease, and desertion.

The Portuguese royal court transferred from Lisbon to the Portuguese colony of Brazil in a strategic retreat of Queen Maria I of Portugal, Prince Regent John, the Braganza royal family, its court, and senior functionaries, totaling nearly 10,000 people, on 27 November 1807. The embarkment took place on the 27th, but due to weather conditions, the ships were only able to depart on the 29 November. The Braganza royal family departed for Brazil just days before Napoleonic forces invaded Lisbon on 1 December. The Portuguese crown remained in Brazil from 1808 until the Liberal Revolution of 1820 led to the return of John VI of Portugal on 26 April 1821.

For thirteen years, Rio de Janeiro, Brazil, functioned as the capital of the Kingdom of Portugal in what some historians call a metropolitan reversal (i.e., a colony exercising governance over the entirety of an empire). The period in which the court was located in Rio brought significant changes to the city and its residents, and can be interpreted through several perspectives. It had profound impacts on Brazilian society, economics, infrastructure, and politics. The transfer of the king and the royal court "represented the first step toward Brazilian independence, since the king immediately opened the ports of Brazil to foreign shipping and turned the colonial capital into the seat of government."

The Peninsular War (1807–1814) was the military conflict fought in the Iberian Peninsula by Spain, Portugal, and the United Kingdom against the invading and occupying forces of the First French Empire during the Napoleonic Wars. In Spain, it is considered to overlap with the Spanish War of Independence. The war started when the French and Spanish armies invaded and occupied Portugal in 1807 by transiting through Spain, and it escalated in 1808 after Napoleonic France had occupied Spain, which had been its ally. Napoleon Bonaparte forced the abdications of Ferdinand VII and his father Charles IV and then installed his brother Joseph Bonaparte on the Spanish throne and promulgated the Bayonne Constitution. Most Spaniards rejected French rule and fought a bloody war to oust them. The war on the peninsula lasted until the Sixth Coalition defeated Napoleon in 1814, and it is regarded as one of the first wars of national liberation and is significant for the emergence of large-scale guerrilla warfare.

The United Kingdom of Portugal, Brazil and the Algarves was a pluricontinental monarchy formed by the elevation of the Portuguese colony named State of Brazil to the status of a kingdom and by the simultaneous union of that Kingdom of Brazil with the Kingdom of Portugal and the Kingdom of the Algarves, constituting a single state consisting of three kingdoms.

The United Kingdom of Portugal, Brazil and the Algarves was formed in 1815, following the transfer of the Portuguese Court to Brazil during the Napoleonic invasions of Portugal, and it continued to exist for about one year after the return of the Court to Europe, being de facto dissolved in 1822, when Brazil proclaimed its independence. The dissolution of the United Kingdom was accepted by Portugal and formalized de jure in 1825, when Portugal recognized the independent Empire of Brazil.

During its period of existence the United Kingdom of Portugal, Brazil and the Algarves did not correspond to the whole of the Portuguese Empire: rather, the United Kingdom was the transatlantic metropolis that controlled the Portuguese colonial empire, with its overseas possessions in Africa and Asia.

Thus, from the point of view of Brazil, the elevation to the rank of a kingdom and the creation of the United Kingdom represented a change in status, from that of a colony to that of an equal member of a political union. In the wake of the Liberal Revolution of 1820 in Portugal, attempts to compromise the autonomy and even the unity of Brazil, led to the breakdown of the union.

The Liberal Revolution of 1820 was a Portuguese political revolution that erupted in 1820. It began with a military insurrection in the city of Porto, in northern Portugal, that quickly and peacefully spread to the rest of the country. The Revolution resulted in the return in 1821 of the Portuguese Court to Portugal from Brazil, where it had fled during the Peninsular War, and initiated a constitutional period in which the 1822 Constitution was ratified and implemented. The movement's liberal ideas had an important influence on Portuguese society and political organization in the nineteenth century.

The Independence of Brazil comprised a series of political and military events that led to the independence of the Kingdom of Brazil from the United Kingdom of Portugal, Brazil and the Algarves as the Brazilian Empire. Most of the events occurred in Bahia, Rio de Janeiro, and São Paulo between 1821–1824. It is celebrated on 7 September, although there is a controversy whether the real independence happened after the Siege of Salvador on July 2 of 1823 in Salvador, Bahia where the independence war was fought. However, September 7th is the anniversary of the date in 1822 that prince regent Dom Pedro declared Brazil's independence from his royal family in Portugal and the former United Kingdom of Portugal, Brazil and Algarves. Formal recognition came with a treaty three years later, signed by the new Empire of Brazil and the Kingdom of Portugal in late 1825.

The War of the Two Brothers was a war between liberal constitutionalists and conservative absolutists in Portugal over royal succession that lasted from 1828 to 1834. Embroiled parties included the Kingdom of Portugal, Portuguese rebels, the United Kingdom, France, the Catholic Church, and Spain.

At the height of European colonialism in the 19th century, Portugal had lost its territory in South America and all but a few bases in Asia. During this phase, Portuguese colonialism focused on expanding its outposts in Africa into nation-sized territories to compete with other European powers there. Portugal pressed into the hinterland of Angola and Mozambique, and explorers Serpa Pinto, Hermenegildo Capelo and Roberto Ivens were among the first Europeans to cross Africa west to east.

During the period of Portuguese colonial rule of Angola, cities, towns and trading posts were founded, railways were opened, ports were built, and a Westernised society was being gradually developed, despite the deep traditional tribal heritage in Angola which the minority European rulers were neither willing nor interested in eradicating.

The 1890 British Ultimatum was an ultimatum by the British government delivered on 11 January 1890 to the Kingdom of Portugal. The ultimatum forced the retreat of Portuguese military forces from areas which had been claimed by Portugal on the basis of historical discovery and recent exploration, but which the United Kingdom claimed on the basis of effective occupation. Portugal had attempted to claim a large area of land between its colonies of Mozambique and Angola including most of present-day Zimbabwe and Zambia and a large part of Malawi, which had been included in Portugal's "Rose-coloured Map".

It has sometimes been claimed that the British government's objections arose because the Portuguese claims clashed with its aspirations to create a Cape to Cairo Railway, linking its colonies from the south of Africa to those in the north. This seems unlikely, as in 1890 Germany already controlled German East Africa, now Tanzania, and Sudan was independent under Muhammad Ahmad. Rather, the British government was pressed into taking action by Cecil Rhodes, whose British South Africa Company was founded in 1888 south of the Zambezi and the African Lakes Company and British missionaries to the north.

The 5 October 1910 revolution was the overthrow of the centuries-old Portuguese monarchy and its replacement by the First Portuguese Republic. It was the result of a coup d'état organized by the Portuguese Republican Party.

By 1910, the Kingdom of Portugal was in deep crisis: national anger over the 1890 British Ultimatum, the royal family's expenses, the assassination of the King and his heir in 1908, changing religious and social views, instability of the two political parties (Progressive and Regenerador), the dictatorship of João Franco, and the regime's apparent inability to adapt to modern times all led to widespread resentment against the Monarchy. The proponents of the republic, particularly the Republican Party, found ways to take advantage of the situation. The Republican Party presented itself as the only one that had a programme that was capable of returning to the country its lost status and place Portugal on the way of progress.

After a reluctance of the military to combat the nearly two thousand soldiers and sailors that rebelled between 3 and 4 October 1910, the Republic was proclaimed at 9 o'clock a.m of the next day from the balcony of the Lisbon City Hall in Lisbon. After the revolution, a provisional government led by Teófilo Braga directed the fate of the country until the approval of the Constitution in 1911 that marked the beginning of the First Republic. Among other things, with the establishment of the republic, national symbols were changed: the national anthem and the flag. The revolution produced some civil and religious liberties.

The First Portuguese Republic spans a complex 16-year period in the history of Portugal, between the end of the period of constitutional monarchy marked by the 5 October 1910 revolution and the 28 May 1926 coup d'état. The latter movement instituted a military dictatorship known as Ditadura Nacional (national dictatorship) that would be followed by the corporatist Estado Novo (new state) regime of António de Oliveira Salazar.

The sixteen years of the First Republic saw nine presidents and 44 ministries, and were altogether more of a transition between the Kingdom of Portugal and the Estado Novo than they were a coherent period of governance.

Portugal did not initially form part of the system of alliances involved in World War I and thus remained neutral at the start of the conflict in 1914. But even though Portugal and Germany remained officially at peace for over a year and a half after the outbreak of World War I, there were many hostile engagements between the two countries. Portugal wanted to comply with British requests for aid and protect its colonies in Africa, causing clashes with German troops in the south of Portuguese Angola, which bordered German South-West Africa, in 1914 and 1915 (see German campaign in Angola). Tensions between Germany and Portugal also arose as a result of German U-boat warfare, which sought to blockade the United Kingdom, at the time the most important market for Portuguese products. Ultimately, tensions resulted in the confiscation of German ships interned in Portuguese ports, to which Germany reacted by declaring war on 9 March 1916, quickly followed by Portugal's reciprocal declaration.

Approximately 12,000 Portuguese troops died during the course of World War I, including Africans who served in its armed forces on the colonial front. Civilian deaths in Portugal exceeded 220,000: 82,000 caused by food shortages and 138,000 by the Spanish flu.

The 28 May 1926 coup d'état, sometimes called 28 May Revolution or, during the period of the authoritarian Estado Novo (English: New State), the National Revolution (Portuguese: Revolução Nacional), was a military coup of a nationalist origin, that put an end to the unstable Portuguese First Republic and initiated 48 years of authoritarian rule in Portugal. The regime that immediately resulted from the coup, the Ditadura Nacional (National Dictatorship), would be later refashioned into the Estado Novo (New State), which in turn would last until the Carnation Revolution in 1974.

The Ditadura Nacional was the name given to the regime that governed Portugal from 1926, after the re-election of General Óscar Carmona to the post of President, until 1933. The preceding period of military dictatorship that started after the 28 May 1926 coup d'état is known as Ditadura Militar (Military Dictatorship). After adopting a new constitution in 1933, the regime changed its name to Estado Novo (New State). The Ditadura Nacional, together with the Estado Novo, forms the historical period of the Portuguese Second Republic (1926–1974).

The Estado Novo was the corporatist Portuguese state installed in 1933. It evolved from the Ditadura Nacional ("National Dictatorship") formed after the coup d'état of 28 May 1926 against the democratic but unstable First Republic. Together, the Ditadura Nacional and the Estado Novo are recognised by historians as the Second Portuguese Republic (Portuguese: Segunda República Portuguesa). The Estado Novo, greatly inspired by conservative, fascist and autocratic ideologies, was developed by António de Oliveira Salazar, who was President of the Council of Ministers from 1932 until illness forced him out of office in 1968.

The Estado Novo was one of the longest-surviving authoritarian regimes in Europe in the 20th century. Opposed to communism, socialism, syndicalism, anarchism, liberalism and anti-colonialism, the regime was conservative, corporatist, nationalist and fascist in nature, defending Portugal's traditional Catholicism. Its policy envisaged the perpetuation of Portugal as a pluricontinental nation under the doctrine of lusotropicalism, with Angola, Mozambique, and other Portuguese territories as extensions of Portugal itself, it being a supposed source of civilization and stability to the overseas societies in the African and Asian possessions. Under the Estado Novo, Portugal tried to perpetuate a vast, centuries-old empire with a total area of 2,168,071 square kilometres (837,097 sq mi), while other former colonial powers had, by this time, largely acceded to global calls for self-determination and independence of their overseas colonies.

Portugal joined the United Nations (UN) in 1955 and was a founding member of NATO (1949), the OECD (1961), and EFTA (1960). In 1968, Marcelo Caetano was appointed prime minister replacing an aged and debilitated Salazar; he continued to pave the way towards economic integration with Europe and an higher level of economic liberalization in the country, achieving the signing of an important free-trade agreement with the European Economic Community (EEC) in 1972.

From 1950 until Salazar's death in 1970, Portugal saw its GDP per capita increase at an annual average rate of 5.7 per cent. Despite the remarkable economic growth, and economic convergence, by the fall of the Estado Novo in 1974, Portugal still had the lowest per capita income and the lowest literacy rate in Western Europe (although this also remained true following the fall, and continues to the present day). On 25 April 1974, the Carnation Revolution in Lisbon, a military coup organized by left-wing Portuguese military officers – the Armed Forces Movement (MFA) – led to the end of the Estado Novo.

At the start of World War II in 1939, the Portuguese Government announced on 1 September that the 550-year-old Anglo-Portuguese Alliance remained intact, but since the British did not seek Portuguese assistance, Portugal was free to remain neutral in the war and would do so. In an aide-mémoire of 5 September 1939, the British Government confirmed the understanding. As Adolf Hitler's occupation swept across Europe, neutral Portugal became one of Europe's last escape routes. Portugal was able to maintain its neutrality until 1944, when a military agreement was signed to give the United States permission to establish a military base in Santa Maria in the Azores and thus its status changed to non-belligerent in favor of the Allies.

The Portuguese Colonial War was a 13-year-long conflict fought between Portugal's military and the emerging nationalist movements in Portugal's African colonies between 1961 and 1974. The Portuguese ultraconservative regime at the time, the Estado Novo, was overthrown by a military coup in 1974, and the change in government brought the conflict to an end. The war was a decisive ideological struggle in Lusophone Africa, surrounding nations, and mainland Portugal.

The Carnation Revolution was a military coup by left-leaning military officers that overthrew the authoritarian Estado Novo regime on 25 April 1974 in Lisbon, producing major social, economic, territorial, demographic, and political changes in Portugal and its overseas colonies through the Processo Revolucionário Em Curso. It resulted in the Portuguese transition to democracy and the end of the Portuguese Colonial War.

The revolution began as a coup organised by the Armed Forces Movement (Portuguese: Movimento das Forças Armadas, MFA), composed of military officers who opposed the regime, but it was soon coupled with an unanticipated, popular civil resistance campaign. Negotiations with African independence movements began, and by the end of 1974, Portuguese troops were withdrawn from Portuguese Guinea, which became a UN member state. This was followed in 1975 by the independence of Cape Verde, Mozambique, São Tomé and Príncipe and Angola in Africa and the declaration of independence of East Timor in Southeast Asia. These events prompted a mass exodus of Portuguese citizens from Portugal's African territories (mostly from Angola and Mozambique), creating over a million Portuguese refugees – the retornados.

The carnation revolution got its name from the fact that almost no shots were fired and from restaurant worker Celeste Caeiro offering carnations to the soldiers when the population took to the streets to celebrate the end of the dictatorship, with other demonstrators following suit and carnations placed in the muzzles of guns and on the soldiers' uniforms. In Portugal, 25 April is a national holiday that commemorates the revolution.