Alphonso VIII became King of Castile in 1158 upon the death of his father. Troubled by interference from navarre in his youth, he later allied Castile with Aragon, forming a connection that was eventually to become the basis for the unification of Spain. He also established Castilian dominance over Leon.

In 1170 he married Eleanor, daughter of King Henry II of England. From the 1170’s, he resisted encroachments by the Almohads, Moslem invaders from nothern Africa. Defeated by the Moslem Caliph, Yakub Al Mansur at Alarcos in 1195, Alphonso and his allies won a major victory over the moslem commander, Al-Nasir, at navas de Tolosa in 1212.