Isabella of Castille was the Queen of Castile and León from 1474 until her death in 1504. She is best known for her role in the unification of Spain and for sponsoring Christopher Columbus's 1492 expedition, which led to the discovery of the Americas. Her reign marked a significant shift toward centralized power in Spain, aligning with the trends of new monarchies that emerged in Europe during the late 15th and early 16th centuries.