The Kingdom of Portugal (Latin: Regnum Portugalliae, Portuguese: Reino de Portugal) was a monarchy on the Iberian Peninsula and the predecessor of modern Portugal. It was in existence from 1139 until 1910. After 1248, it was also known as the Kingdom of Portugal and the Algarves, and between 1815 and 1822, it was part of the United Kingdom of Portugal, Brazil and the Algarves. The name is also often applied to the Portuguese Empire, the realm's extensive overseas colonies.
The nucleus of the Portuguese state was the County of Portugal, established in the 9th century as part of the Reconquista, by Vímara Peres, a vassal of the King of Asturias. The county became part of the Kingdom of León in 1097, and the Counts of Portugal established themselves as rulers of an independent kingdom in the 12th century, following the battle of São Mamede. The kingdom was ruled by the Alfonsine Dynasty until the 1383-85 Crisis, after which the monarchy passed to the House of Aviz.
During the 15th and 16th century, Portuguese exploration established a vast colonial empire. From 1580 to 1640, the Kingdom of Portugal was in personal union with Habsburg Spain.
After the Portuguese Restoration War of 1640-1668, the kingdom passed to the House of Braganza and thereafter to the House of Braganza-Saxe-Coburg and Gotha. From this time, the influence of Portugal declined, but it remained a major power due to its most valuable colony, Brazil. After the independence of Brazil, Portugal sought to establish itself in Africa, but was ultimately forced to yield to the British interests, leading to the collapse of the monarchy in the 5 October 1910 revolution and the establishment of the First Portuguese Republic.
Portugal was a decisive absolute monarchy before 1822. It rotated between absolute and constitutional monarchy from 1822 until 1834, and was a decisive constitutional monarchy after 1834.