On December 25, 1978, the armed forces of Vietnam launched a full-scale invasion of Cambodia. That event marked a turning point in the first and only extended war fought between two communist regimes. The Vietnamese forced out Pol Pot s Khmers Rouge 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. At its core are two separate but related histories covering the years 1930 to 1978. The first concerns the continuing difficult relations between the Vietnamese communist party and the Cambodian communist movement. The second records the fluctuating and often conflicted relations between the Vietnamese communist party and the two most powerful communist states, the Soviet Union and China. These two histories are encased by a theoretical introduction and a conclusion that make clear the need for a political culture perspective on international relations.