Isabella of Castile and Ferdinand of Aragon united their kingdoms through marriage in 1469, establishing 150 years of joint rule. They faced civil war in Castile over succession, which Isabella won with Aragonese support. As the Catholic Monarchs, they pursued religious unity, expelling Jews in 1492 and forcing Muslims to convert. They conquered Granada in 1492, ending Muslim rule in Iberia. Their empire expanded through Columbus' voyages and the Treaty of Tordesillas. Reforms centralized power under their dynastic rule, laying the foundations for a global Spanish empire.