The Capetians next moved to take over the rich Mediterranean south. Its people belonged to the heretical church of the Cathars, with its center at the town of Albi. Hence, they were called Albigensians. They believed that the history of the universe was one long struggle between the forces of light (good) and the forces of darkness (evil).
The evil forces (Satan) created man and the earth, but Adam had some measure of goodness. Jesus was not born of a woman, nor was he crucified, because he was wholly good, wholly light. The Jehovah of the Old Testament was the god of evil. Albigensians often had the support of nobles, and particularly women, who adopted their views to combat the church politically. The church proclaimed a Crusade against the Albigensians in 1208.
Philip Augustus did not at first participate in the expeditions of his nobles, who rushed south to plunder in the name of the Catholic Church. Northern French nobles were soon staking out their claims to the lands of southern French nobles who embraced the heresy. By the year of Philip’s death (1223), after the war had gone on intermittently for fourteen years, the territorial issue had become confounded with the religious one.
So Philip sponsored an expedition led by his son, Louis VIII (r. 1223-1226). Assisted by a special clerical court called the Inquisition, Louis VIII and his son Louis IX (r. 1226-1270) carried on the campaign. The south was almost entirely taken over by the Crown, and it was arranged that the lands of the count of Toulouse, the greatest lord in the region, would come by marriage to the brother of the king of France when the last count died.