On December 25, 1978, the armed forces of Vietnam launched a full-scale invasion of Cambodia that marked a turning point in the first and only extended war fought between two communist regimes. The Vietnamese forced Pol Pot's Khmers Rouges regime from its seat of power in Phnom Penh, but the ensuing war was a major source of international tension throughout the last decade of the Cold War.

This book is the first comprehensive, scholarly analysis of the causes of the Vietnamese invasion, and it is the only study of Southeast Asian affairs by a Western scholar who has made use of the rich archives of the former Communist Party of the Soviet Union.