Spanish Unification refers to the process in the late 15th century when the kingdoms of Castile and Aragon united under the rule of Isabella I of Castile and Ferdinand II of Aragon. This marriage in 1469 laid the foundation for a unified Spain, promoting political stability and centralization of power. The unification was further solidified with the completion of the Reconquista in 1492, which expelled the Moors from the Iberian Peninsula. This period also marked the beginning of Spain's rise as a global power, leading to exploration and colonization in the Americas.