In 1985, McAdams notes, 38 percent of the world’s population lived under communist regimes. Some 107 communist parties operated worldwide, with a total membership of 82 million people. McAdams tells the story of how this movement grew out of the crucible of nineteenth-century Europe, flourished in the Soviet Union, and then spread to China, Cuba, and beyond. He starts with Marx and Engels, explaining how their revolutionary ideas triumphed over the other political and intellectual currents of their day. He then turns to Vladimir Lenin and the party he created, its early European offshoots, and the Comintern—which, for a time, allowed the movement to remain somewhat monolithic. This, however, is not merely descriptive history. McAdams wrestles with a more profound puzzle: How was it, given the failure of Marx’s prophecies, that his ideas continued to animate communist parties and eventually led them to power in 24 countries? McAdams points to the sense of historical destiny and transcendence that Marxism inspired and also to the qualities of the Communist Party: its arrogated primacy, the requirements it set for its members, its rigid mission. All of that depended, of course, on the leaders who forged the movement: Lenin, Joseph Stalin, Mao Zedong, and Fidel Castro.