This led to accusations of Gnosticism and attracted the ire of the Catholic establishment. Several of their practices, especially their belief in the inherent evil of the physical world, conflicted with the doctrines of the Incarnation of Christ and Catholic sacraments.

Their theology, neo-Gnostic in many ways, was basically dualist. The reforms were a reaction against the often perceived scandalous and dissolute lifestyles of the Catholic clergy in southern France. The Cathars originated from an anti-materialist reform movement within the Bogomil churches of the Balkans calling for what they saw as a return to the Christian message of perfection, poverty and preaching, combined with a rejection of the physical to the point of starvation. The Crusade was prosecuted primarily by the French crown and promptly took on a political aspect, resulting in not only a significant reduction in the number of practising Cathars, but also a realignment of the County of Toulouse in Languedoc, bringing it into the sphere of the French crown, and diminishing both Languedoc's distinct regional culture and the influence of the counts of Barcelona. The Albigensian Crusade or the Cathar Crusade (1209–1229 French: Croisade des albigeois, Occitan: Crosada dels albigeses) was a 20-year military campaign initiated by Pope Innocent III to eliminate Catharism in Languedoc, in southern France.

Brutal heretic