Here the great Catholic historian Hilaire Belloc analyzes 5 of the greatest heresies of all time: Arianism, Mohammedanism (Islam), Albigensianism, Protestantism, and "the Modern Attack," showing that the world would be vastly different today if Arianism or Albigensianism had survived--and how it is different because Protestantism survived. He predicts the re-emergence of Islam; explains how the Modern Attack is the worst threat to the Catholic Church ever.