What is special about the process of unification of Spain?

Modern Spain, a very beautiful country with many nationalities. But it was not always so. It should be noted that the history of the country of Spain begins with an attempt to unite the two largest kingdoms of the Iberian Peninsula, which are called Aragon and Castile. Initially, a unified Spain was a union of these two kingdoms. Foreign policy became a factor for the unification of the kingdoms. Joint armies in 1492 defeated the last Moorish state on the territory of the Iberian Peninsula called Granada.