As usual in such cases, religion went hand in hand with culture and economics. Protected by rich independent Toulousian Counts Raymond VI and VII, the regions supporting Catharism were precisely those whose inhabitants made very good money dying cloth with the famous dyer's woad (a plant producing a uniquely appealing blue tint) that they exported to the Levant from the Toulousian port of Narbonne.
In 1150 St. Bernard, the good cop, arrived to convert the Cathars but met with minimal success. In 1207, bad-cop Pope Innocent III asked Raymond VI to withdraw his protection, and when Raymond refused, excommunicated him. That too having little effect, in 1208 Innocent III preached a crusade against the Languedoc. This was little more than open season for a land grab, with barons, dukes, counts and their armies coming south to wipe out heresy and augment their own lands. During the next twenty years, Languedoc was ravaged - in 1209 30,000 residents of Beziers were slaughtered. Raymond VI was captured and most towns succumbed, but as soon as the armies withdrew, Catharism resurfaced. In 1226 the Second Albigensian Crusade was preached, under the command of Louis VIII, King of France, and in 1231 the Inquisition added its gentle ministrations to the fight against heresy. In 1244 the last major fortress, Montsegur, was taken and its garrison of 215 unrepentant Cathars burned alive. In 1256 Catharism was finally eradicated when Queribus fell.