The Crown of Castile was a significant medieval kingdom in the Iberian Peninsula, which later became part of modern-day Spain. It emerged in the 11th century and played a crucial role in the unification of Spain. The crown was known for its strong monarchy and influential nobility, contributing to the political and cultural landscape of the region. In 1469, the marriage of Isabella I of Castile and Ferdinand II of Aragon united the two crowns, leading to the formation of a more centralized Spanish state. This union marked the beginning of the Spanish Empire, which expanded significantly in the following centuries, influencing global history.