Christian Spain from the Muslim invasion to about 1260
Despite ongoing warfare among its various Christian kingdoms, a recurring theme in Christian Spain from the Islamic invasion of the 8th century to the coming of the Catholic Monarchs, Ferdinand and Isabella, in the late 15th century was the unification of the Iberian Peninsula under Christian rule. The Islamic conquest disrupted whatever measure of unity the Visigoths had achieved and raised new religious, cultural, legal, linguistic, and ethnic barriers to assimilation with the native population. A number of tiny Christian states eventually rose from obscurity in the northern mountains and, prompted by self-preservation and religio-cultural hostility toward Islam, initiated the Reconquista (Reconquest). Christian success was in direct proportion to the strength of Islamic Spain at any given time. When Islamic power waned, the Christians usually advanced their frontiers. The kings of Asturias-León-Castile, declaring themselves the heirs of the Visigoths, claimed hegemony over the entire peninsula. However, the rulers of Portugal, Navarre (Navarra), and Aragon-Catalonia (Spanish: Cataluña; Catalan: Catalunya), whose frontiers began to be delineated in the 11th and 12th centuries, repudiated and often undermined the aspirations of their larger neighbour. The Reconquista was nearly completed by the middle of the 13th century, by which time the Muslims retained only the small kingdom of Granada (Arabic: Gharnāṭah) in vassalage to Castile until 1492.
The Trastámara dynasty, which came to power in Castile in the late 14th century, gave a new impetus to the search for peninsular unity by using marriage, diplomacy, and war to acquire dominion over the neighbouring Christian kingdoms. At the same time, the Trastámaras struggled to extend royal power against the resistance of the nobles. Ferdinand and Isabella linked Aragon and Castile by marriage and also brought the Reconquista to a conclusion by conquering Granada. However, as they were unable to incorporate Portugal into a family union by marriage, the unification of the peninsula was incomplete. The political union of Castile and Aragon could not by itself, of course, overcome the two realms’ centuries-old diversity of languages, laws, and traditions.