Struggle for the throne of Portugal

The Portuguese succession crisis of 1580 (Portuguese: Crise de sucessão de 1580) came about as a result of the death of young King Sebastian I of Portugal in the Battle of Alcácer Quibir in 1578. As Sebastian had no immediate heirs, this event prompted a dynastic crisis, with internal and external battles between several pretenders to the Portuguese throne; in addition, because Sebastian's body was never found, several impostors emerged over the next several years claiming to be the young king, further confusing the situation. Ultimately, Philip II of Spain gained control of the country, uniting the Portuguese and Spanish Crowns in the Iberian Union, a personal union that would last for 60 years, during which time the Portuguese Empire declined.

The Cardinal Henry, Sebastian's great-uncle, became ruler in the immediate wake of Sebastian's death. Henry had served as regent for Sebastian after 1562, 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.

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:

The Duchess would later be acknowledged as the legitimate heir, after her descendants obtained the throne in 1640 (in the person of her grandson John IV of Portugal), but at that time, she was only one of several possible heirs. The heir by primogeniture was her nephew Ranuccio Farnese, being the son of Catherine's late older sister Maria, followed by his siblings; then the Duchess herself and her children; and only after them, King Philip. Philip II was a foreigner (although his mother was Portuguese) and descended from Manuel I by a female line; as for Anthony, although he was Manuel I's grandson in the male line, he was of illegitimate birth.

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