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.