The monarchs began a series of campaigns known as the Granada War (1482–1492), which was aided by Pope Sixtus IV's granting the tithe revenue and implementing a crusade tax so that the monarchs could finance the war. After 10 years of fighting the Granada War ended in 1492 when Emir Boabdil surrendered the keys of the Alhambra Palace in Granada to the Castilian soldiers. With the fall of Granada in January 1492, Isabella and Ferdinand pursued further policies of religious unification of their realms, in particular the expulsion of Jews who refused to convert to Christianity.