The Cathar Crusade, also known as the Albigensian Crusade, was a military campaign initiated by the Catholic Church in the early 13th century to eliminate the Cathar heresy in southern France. The Cathars, who believed in dualism and rejected the authority of the Church, posed a significant challenge to the Catholic faith. The crusade began in 1209 and lasted for about 20 years, resulting in widespread violence and the destruction of many towns. The conflict was marked by brutal battles and the establishment of the Inquisition to root out heretics. Key figures included Simon de Montfort, who led the crusaders, and Pope Innocent III, who called for the campaign. The crusade ultimately led to the decline of Catharism and increased the power of the Catholic Church in the region.