The Cambodian–Vietnamese War was an armed conflict from 1978 to 1989 between the Khmer Rouge and Vietnam, and their respective allies. It began in December 1978, with a Vietnamese invasion of Cambodia which toppled the Khmer Rouge and ended in 1989 with the withdrawal of Vietnamese forces from Cambodia. This Cold War conflict was part of the Third Indochina War and Sino-Soviet split with the Soviet Union supporting Vietnam and China supporting the Khmer Rouge.
Despite both being communist, the alliance between the Communist Party of Vietnam and the Khmer Rouge broke down after both defeated Vietnamese and Cambodian anti-communist regimes respectively in the Vietnam War. As a result, the war was preceded by years of conflict between Vietnam and the Khmer Rouge, led by Pol Pot, when the Khmer Rouge ruled Democratic Kampuchea repeatedly invaded Vietnam, including massacres by the Khmer Rouge, notably the Ba Chúc massacre of over 3,000 Vietnamese civilians in April 1978. On 21 December 1978, the Vietnamese launched a limited offensive towards the town of Kratie. On 23 December 1978, 10 out of 19 divisions of the Khmer Rouge's Kampuchea Revolutionary Army opened fire along the border with Vietnam with the goal of invading the southwestern border provinces of Đồng Tháp, An Giang and Kiên Giang. On 25 December 1978, Vietnam supported Cambodian dissidents in exile and launched a full-scale invasion of Kampuchea, occupying the country in two weeks, capturing the capital Phnom Penh, and removing the Khmer Rouge government of the Communist Party of Kampuchea from power. In doing so, Vietnam put an ultimate stop to the Cambodian genocide which had killed between 1.2 and 2.8 million people or between 13 and 30 percent of the country's population since 1975. However, the Khmer Rouge regime maintained its membership in the United Nations and the war isolated Vietnam from the international community except the Eastern Bloc. The Vietnamese occupation caused discontent among Cambodians.
