Isabella I of Castile, alongside her husband Ferdinand II of Aragon, is credited for uniting the two kingdoms in the late 15th century. Their marriage in 1469 was a strategic alliance that laid the foundation for the unification of Spain. Under their reign, the Spanish Inquisition was established, and they completed the Reconquista by conquering Granada in 1492. Isabella and Ferdinand also sponsored Christopher Columbus's voyage to the New World, which marked the beginning of Spain's vast overseas empire. Their joint reign is often seen as a pivotal moment in Spanish history, leading to the emergence of Spain as a major European power.