When Marx and Engels published The Communist Manifesto in the 1840s, they hatched an idea that would grow in ways that they could scarcely have imagined. Here A. James McAdams shows how the leaders of the Soviet Union, China, Germany, Yugoslavia, Cuba, and North Korea adapted communism to mesmerize their followers and transform their societies, but also to justify acts of inhumanity. McAdams explains why communist parties lasted as long as they did, and why they ceased to be meaningful institutions by the close of the 20th century.