In mid-1945, as Allied forces pushed toward victory in the Pacific, American political leaders faced a deepening dilemma. They could continue to work with both Mao Zedong’s Communist insurgents and the Nationalist Party of Chiang Kai-shek (aka “the Generalissimo”), preparing for a postwar order based on some kind of coalition government in China. Or they could tilt unequivocally toward Chiang, who was still nominally China’s head of state but controlled only those parts of the country not under the thumb of the Japanese military or the Red Army. Some well-informed American “China hands,” both in the field and back in...