Cathars

Cathars were a very successful medieval gnostic Christian sect, or heresy from the Catholic perspective, that flourished mainly, but not exclusively, in the southern region of France known as Languedoc, in the tenth through the twelfth centuries. The popularity of the Cathar religion was so great that it practically became the state religion of the Languedoc region at the time. This widespread popularity proved to be a very clear threat to the Catholic Church. Pope Innocent III instigated a campaign to destroy them; this campaign eventually led to the Inquisition which spread across Europe, and, in reality, still exists today. Historians have recognized this war against the pacifist Cathar heresy as the first genocide of Christians by Christians.