The Cathar Crusade
The entanglement of the Church with the world after the liberation from ties to the world led to the establishment of sects which denied the Church's rights to rule and possess properties and which demanded apostolic poverty.
The Cathari sect developed out of the Bogomils of Bulgaria and the movement of migrating heretics to France.
The Cathar Crusade (1209-1229) was a 20-year murderous military campaign initiated by the Catholic Church to eliminate the Cathar heresy in Languedoc. With the support of the northern French aristocracy and the clerics the Roman Church achieved the complete extermination of the enemy. (Over 100,000 cathari murdered)
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The Cathar Crusade from Wikipedia