In the 5th century, Germanic barbarian tribes, most notably the Suevi and the Visigoths, invaded the Iberian peninsula, set up kingdoms, and became assimilated.

An Islamic invasion took place in 711. Many of the ousted nobles took refuge in the unconquered north Asturian highlands. From there they aimed to reconquer their lands from the Moors. In 868, Count Vímara Peres reconquered and governed the region between the Minho and Douro rivers. The county became known as Portucale (i.e. Portugal).

While a dependency of the Kingdom of Leon, Portugal occasionally gained de facto independence during weak Leonese reigns. Then at the end of the 11th century, a knight from Burgundy named Henry became Count of Portugal as a payment for military services to Leon. Henry declared Portugal independent while a war raged between Leon and Castile. Henry died and his son, Afonso Henriques (Afonso I), took control of the county. The city of Braga, the Catholic center of the Iberian Peninsula, faced new competition from other regions. The lords of the cities of Coimbra and Porto, together with the clergy of Braga, demanded the independence of the county.

Portugal traces its emergence as a nation to June 24, 1128, with the Battle of São Mamede by Afonso I. On October 5, 1143, Portugal was formally recognized. Afonso, aided by the Templar Knights, continued to conquer southern lands from the Moors. In 1250, the Portuguese Reconquista ended when it reached the southern coast of Algarve.

In an era of several wars when Portugal and Castile tried to control one another, King Ferdinand was dying with no male heirs. His only child, a single daughter, married King John I of Castile who would therefore be the King of Portugal after Fernando's death. However, the impending loss of independence to Castile was not accepted by the majority of the Portuguese people, which led to the 1383-1385 Crisis. A loyalist faction led by John of Aviz (later John I), with the help of Nuno Álvares Pereira, finally defeated the Castilians in Portugal's most historic battle of Portugal, the Battle of Aljubarrota. The victorious John was then acclaimed as king by the people.

In the meantime, the Black Death reached Portugal.