Treaty of Alcacovas

The Treaty of Alcacovas was concluded in 1479 between the Crown of Castile and the Kingdom of Portugal, bringing to an end the War of the Castilian Succession. That conflict had pitted Isabella I, supported by her husband Ferdinand of Aragon, against her rival Joanna la Beltraneja, whose claim to the Castilian throne was backed by King Afonso V of Portugal.

Under the terms of the treaty, Portugal abandoned its support for Joanna and renounced its claim to the Castilian throne, while also relinquishing its pretensions to the Canary Islands, which were confirmed as Castilian. In return, Castile recognized Portuguese supremacy over the Azores, Madeira, and the Cape Verde islands, as well as Portugal's exclusive rights along the coasts of West Africa and the lucrative Guinea trade.

The Treaty of Alcacovas thus secured Isabella's position on the Castilian throne and was one of the earliest agreements to divide overseas spheres of influence between two European crowns. By confirming Portuguese dominance in the Atlantic south of the Canaries, it shaped the course of subsequent exploration and helped set the stage for the later Treaty of Tordesillas of 1494, which partitioned the wider world between Spain and Portugal.