A Most Holy War - The Albigensian Crusade and the Battle for Christendom

Pegg's narrative of the massacres of the crusades - a fervour of 'cleansing' the world of heresy, and a fear that Christendom was being eaten away by heretics - is gripping. Innocent III's holy genocidal war fundamentally changed how Western civilization dealt with individuals accused of corrupting society, and led to the creation of the inquisition.