How did Castile and Aragon unite for form Spain?

Castile and Aragon united to form Spain primarily through the marriage of Ferdinand II of Aragon and Isabella I of Castile in 1469. This dynastic union effectively linked the two powerful kingdoms, leading to a centralized Spanish monarchy. Their reign marked the completion of the Reconquista in 1492 with the capture of Granada and the establishment of a unified Spanish state, paving the way for Spain's future as a global empire. The political and religious consolidation under their rule also fostered a sense of national identity.