When China’s Cultural Revolution began in 1966, the Red Guards were at its forefront. Under the spell of propaganda and nationalism, with the goal of helping Mao Zedong spread the red sprout of communism, the Red Guards—mostly adolescents, some as young as 14 —started an assault on China’s society and its elites, from party leaders to teachers. Asked to destroy the “Four Olds” (old ideas, old culture, old habits, and old customs), the Red Guards picked their targets, whether philosopher Confucius or military leader Lin Biao, based on both direction from the top and their own local vendettas and whims....