When Chinese officials and elites berate Japan, as they frequently do these days, they often pointedly mention the atrocities that Imperial Japan committed after invading their country in the 1930s. In March, Qin Gang, then China’s foreign minister, warned the Japanese that forgetting their history meant denying crimes that they then might repeat. China’s paramount leader, Xi Jinping, uses the memory of World War II to justify the present-day bluster of a rising global power. “Chinese people who have made such a great sacrifice,” Xi said in 2014, “will not waver in protecting a history written in sacrifice and blood.” When nationalistic Japanese politicians such as Shinzo Abe and Junichiro Koizumi have paid their respects at a Tokyo shrine whose honorees include convicted war criminals, Chinese patriots have exploded with state-sanctioned rage. One reason that East Asia’s two greatest economic powers are still sparring about a bygone war is that the most important international attempt to confront that past—the Tokyo war-crimes trial after World War II—failed to promote a common understanding of who was guilty …