Hilaire Belloc examines the five most destructive heretical movements to have affected Christian Civilization: Arianism, Mohammedanism (Islam), Albigensianism (Cathar), The Reformation (Protestant), and "The Modern Phase." Belloc describes how these movements began, how they spread, and how they continued to influence the world up until the time of his writing (1936). The Chapter on Islam is especially relevant in light of current events; in it Belloc accurately predicts the renewal of Jihadist aggression towards Western Civilization.