War of the Portuguese Succession The War of the Portuguese Succession 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 Philip II of Spain , who eventually succeeded in claiming the crown , reigning as Philip I of Portugal . The Cardinal - King . The Cardinal Henry , great - uncle of Sebastian I of Portugal , became ruler in the immediate wake of Sebastian ' s death . Henry had served as regent for Sebastian after 1557 , and succeeded him as King after the disastrous Battle of Alcácer Quibir in 1578 . Henry renounced his clerical offices and sought to take a bride for the continuation of the Aviz dynasty , but Pope Gregory XIII , affiliated with the Habsburgs , did not release him from his vows . The Cardinal - King died two years later , without having appointed a Council of Regency to choose a successor . Claimants to the throne . Portuguese nobility was worried about the maintenance of their independence and sought help to find a new King . By this time the Portuguese throne was disputed by several claimants ; among them were Catherine , Duchess of Braganza ( 1540 – 1614 ) , her nephew Ranuccio I Farnese , Duke of Parma , Philip II of Spain and António , Prior of Crato . The Duchess was later acknowledged by the Habsburgs as the legitimate heir , after her descendants obtained the throne in 1640 ( in the person of John IV of Portugal ) , but at that time , she was only one of several possible heirs . According to the feudal custom , her late older sister ' s son Rainuccio , an Italian , was the closest heir , then the Duchess herself , and only after them , King Philip . Philip II of Spain was a foreigner ( although his mother was Portuguese ) and descended from Manuel I by a female line ; as for António , although he was Manuel I ' s grandson in the male line , he was an illegitimate grandson . Ranuccio Farnese ( 1569 – 1622 ) , the hereditary Duke of Parma and Piacenza , was the son of the late elder daughter of Duarte of Portugal , Duke of Guimarães , the only son of Manuel I whose legitimate descendants survived at that time , Ranuccio was according to the feudal custom the first heir to the throne of Portugal . He was the son of Don Alexander Farnese , Duke of Parma and Piacenza and of Maria of Portugal . His great - uncle Henry I of Portugal ' s death triggered the struggle for the throne of Portugal when Ranuccio was 11 years old . However , his father was an ally and even a subject of the Spanish King , another contender , so Ranuccio ' s rights were not very forcibly claimed at that time . Ranuccio became reigning Duke of Parma in 1592 . Instead , Ranuccio ' s mother ' s younger sister Catherine , Duchess of Braganza , claimed the throne , very ambitiously , but failed . Catherine , Duchess of Braganza was married to Duke John I of Braganza ( descendant in male line from Afonso , 1st Duke of Braganza , an illegitimate son of John I of Portugal ) , who himself was grandson of the late Duke James of Braganza , also a legitimate heir of Portugal , being the son of infanta Isabella of Portugal , sister of Manuel I and daughter of infante Ferdinand , Duke of Viseu , second son of King Duarte I . The Duchess also had a son , Dom Teodósio of Braganza , who would be her royal heir and successor to the throne . The Duchess ' s claim was relatively strong , as it was reinforced by her husband ' s position as one of the legitimate heirs ; thus they would both be entitled to hold the Kingship . Moreover , the Duchess was living in Portugal , not abroad , and was not underage , but 40 years old . Her weaknesses were her gender ( Portugal had not had a generally recognized reigning queen ) and her being the second daughter , there thus existed a genealogically senior claimant . According to the old feudal custom , the line of succession of the Portuguese throne would have been : Succession . Both António and Philip were the grandchildren of King Manuel I of Portugal : War . On July 24 , 1580 , António proclaimed himself as King of Portugal and of the Algarves , in Santarém , which was followed by popular acclamation in several locations of the country . However , he governed in Continental Portugal for only 33 days , culminating in his defeat at the Battle of Alcântara by the Spanish armies led by Fernando Álvarez de Toledo , Duke of Alba on August 25 . The Battle ended in a decisive victory for the Spanish Habsburgs , both on land and sea . Two days later , the Duke of Alba captured Lisbon . In early 1581 , António fled to France and , as Philip ’ s armies had not yet occupied the Azores , he sailed there with a number of French adventurers under Filippo Strozzi , a Florentine exile in the service of France , but was utterly defeated at sea by a combined Spanish - Portuguese navy commanded by Don Álvaro de Bazán , 1st Marquis of Santa Cruz at the Battle of Ponta Delgada off Terceira Island on July 26 , 1582 and off São Miguel Island on July 27 , 1582 . António still accompanied an English Expedition , under the command of Sir Francis Drake and Sir John Norreys , to the coasts of Spain and Portugal but the Expedition failed and António ' s attempt to rule Portugal from Terceira Island , in the Azores ( where he even minted coins ) came to an end in 1583 . Consequences . The combined Spanish - Portuguese navy ' s victory resulted in the rapid Spanish conquest of the Azores , completing the union of the Portuguese and Spanish empires . The King Philip II of Spain was recognized as King Philip I of Portugal and of the Algarves by the Portuguese Cortes of Tomar ( 1581 ) . Spain and Portugal would remain united in a personal union of the crowns ( remaining formally independent and with autonomous administrations ) for the next 60 years , until 1640 . This period is called the Iberian Union .