Alfonso III of Asturias repopulated the strategically important city Leon and established it as his capital. King Alfonso began a series of campaigns to establish control over all the lands north of the Douro river. He reorganized his territories into the major duchies (Galicia and Portugal) and major counties (Saldaña and Castile), and fortified the borders with many castles. When the Asturian king, Alfonso the Great was deposed, his kingdom was divided among the three sons of Alfonso III of Asturias: García (León), Ordoño (Galicia) and Fruela (Asturias). In 924, Galicia and Asturias was conquered thus forming the Kingdom of Leon.

The Caliphate of Córdoba was gaining power, and began to attack Leon. King Ordoño allied with Navarre against Abd-al-Rahman, but they were defeated in Valdejunquera in 920. For the next 80 years, the Kingdom of León suffered civil wars, Moorish attack, internal intrigues and assassinations, and the partial independence of Galicia and Castile, thus delaying the reconquest and weakening the Christian forces. It was not until the following century that the Christians started to see their conquests as part of a long-term effort to restore the unity of the Visigothic kingdom.