The international order in East Asia changed dramatically following the conclusion of the Sino-Japanese War in 1945; the two most consequential events of this period were the birth of the People’s Republic of China (PRC) on October 1, 1949, and, one year later, the PRC’s entry into a three-year military contest against the United States in the Korean War, 1950–53. These developments confirmed the spread of the Cold War to East Asia and determined the long-term pattern of confrontation between the United States and the Soviet Union in the region. For China, the decision to ally with the USSR and enter the Korean War meant that there was no alternative but to man Asia’s Cold War frontier against US encroachment. All developments accompanying the birth of the PRC and its choice of foreign policies — especially the decision to enter the Korean War — were deeply rooted in China’s domestic politics, and it can be safely concluded that the leaders of the Chinese Communist Party (CCP) made coherent choices when confronted with international crises. Yet the contest between the United States and the Soviet Union rapidly grew into the most significant characteristic of the postwar international system, and greatly infiuenced the future of China. From 1945, it was the interaction between four actors — the United States, the USSR, the Guomindang (GMD), and the CCP — that constituted the fundamental interface between Chinese domestic politics and the international system. It was also this dynamic that pushed China into deeper and deeper involvement in the Cold War.