Communist movement in Cambodia (Kampuchea) that formed the largest opposition group to the US-backed regime led by Lon Nol 1970-75. By 1974 the Khmer Rouge controlled the countryside, and in 1975 the capital, Phnom Penh, was captured and Sihanouk installed as head of state. Internal disagreements led to the creation of the Pol Pot government 1976 and mass deportations and executions. From 1978, when Vietnam invaded the country, the Khmer Rouge conducted a guerrilla campaign against the Vietnamese forces. Pol Pot retired as military leader 1985 and was succeeded by the more moderate Khieu Samphan. Folllowing the withdrawal of Vietnamese forces in 1989, the Khmer Rouge continued its warfare against the Vietnamese-backed government.