In France the Cathars grew to represent a popular mass movement and the belief was spreading to other areas. The Cathar Crusade was initiated by the Roman Catholic Church to eliminate the Cathar heresy in Languedoc. Heresy was a major justification for the Inquisition (Inquisitio Haereticae Pravitatis, Inquiry on Heretical Perversity) and for the European wars of religion associated with the Protestant Reformation.

In what country did the Cathars grow to represent a popular movement?