Vietnam invades Cambodia and topples the Khmer Rouge

On Christmas Day 1978 Vietnam sent a large army into Cambodia, together with Cambodian exiles who had fled the Khmer Rouge. They took Phnom Penh on 7 January 1979 and drove the Khmer Rouge into the western jungles. Vietnam installed a new government under Heng Samrin, called the People's Republic of Kampuchea. The invasion ended the regime responsible for the deaths of well over a million Cambodians.¹²

Relations between the two communist neighbors had turned hostile soon after 1975. The Khmer Rouge, driven by extreme nationalism, raided Vietnamese border villages and claimed lands in the Mekong delta, and purged its own members suspected of Vietnamese ties. Vietnam, meanwhile, had sided with the Soviet Union, while Cambodia sided with China. After a series of border battles in 1977 and 1978, Hanoi decided to topple Pol Pot. China saw the invasion as an attack on its ally and a Soviet gain, and on 17 February 1979 sent troops into northern Vietnam for about four weeks, in what it called a lesson. Both sides claimed victory, and the war left many thousands dead.¹

Vietnam kept some 150,000 troops in Cambodia until 1989, which cost it dearly. China and many Western and Southeast Asian states backed a coalition that included the Khmer Rouge, which kept Cambodia's seat at the United Nations throughout the 1980s. Vietnam was isolated, and under trade embargo. This stalemate eventually led to the negotiated settlement of the early 1990s.¹²