The Cathars believed that God was nothing but spirit and goodness and so could not have created the earthly world, full of pain and violence. Only the Devil could be regarded as the creator and responsible for this evil.
Even though this dualist view of the world was understandable given the anxieties of a population in the throws of spiritual turmoil, it could not be tolerated by the Catholic Church, which ultimately commanded that a crusade be made against it. This began in 1209 and did not really end until 1325.
The Cathar faith was regarded as all the more subversive because it rejected property and contested the pomp of the Church. It held that every person had to free himself from his fleshly prison and raise his soul to God. Only a spiritual sacrament, the Consolamentum, made this reunification possible. It was administered to those credentes (believers) who requested it after a period of initiation. Those who received the Consolamentum assumed the status of Perfect. The Perfecti and Perfectae lived an ascetic, communal life and observed a vow of chastity.
The humble credentes lived an ordinary life secure in the knowledge that on their deathbed they would receive the Consolamentum.
The Cathars travelled widely, preaching all over Europe, but most Cathars lived in Occitania. In towns such as Béziers, Carcassonne, Toulouse, Albi and Foix, along with many other places in Midi-Pyrénées, they found that people were receptive to their ideas in increasing numbers, at all levels of medieval society: peasants, merchants and aristocrats.
The wealth of the bishops, the negligence of the Church, the oppression of onerous taxes: there were many reasons for the people to feel discontented, and the Cathar doctrine, which advocated a return to destitution, alleviated the profound feeling of malaise. Once these ideas had been in circulation for a long time, Catharism grew to become a widespread movement of opposition to the dominant powers.
The local nobility also embraced the Cathar ideal, to the point where they took up arms to defend it. As a result, the counts of Toulouse, Foix and Mirepoix fought on the side of the Cathars during the long years of the crusade.