The authors examine the complex relations between Stalin, Chiang Kai-shek, and Mao during the last year of the Chinese civil war and the emergence of the Cold War. They show how the interplay of perceptions, national security policies, and personalities shaped those relations and were used by the North Korean leader Kim Il Sung to win backing for the invasion of South Korea. The authors also examine the Sino-Soviet alliance, drawing on hitherto unknown secret protocols and understandings and the records of high-level planning that led to the invasion and to the Chinese intervention in Korea. The book is illustrated with 42 photographs and two maps and is the fourth volume in the series, Studies in International Security and Arms Control, sponsored by the Center for International Security and Arms Control at Stanford University.