The Cambodian genocide was the systematic persecution and killing of Cambodian citizens by the Khmer Rouge under the leadership of Communist Party of Kampuchea general secretary Pol Pot. It resulted in the deaths of 1.5 to 2 million people from 1975 to 1979, nearly a quarter of Cambodia's population in 1975 (c. 7.8 million).^[89] The massacres ended when the Vietnamese military invaded in 1978 and toppled the Khmer Rouge regime. By January 1979, 1.5 to 2 million people had died due to the Khmer Rouge's policies, including 200,000–300,000 Chinese Cambodians, 90,000–500,000 Cambodian Cham (who are mostly Muslim),^[90] and 20,000 Vietnamese Cambodians.^[91] 20,000 people passed through the Security Prison 21, one of the 196 prisons the Khmer Rouge operated,^[92] and only seven adults survived.^[93] The prisoners were taken to the Killing Fields, where they were executed (often with pickaxes, to save bullets)^[94] and buried in mass graves. Abduction and indoctrination of children was widespread, and many were persuaded or forced to commit atrocities.^[95] As of 2009, the Documentation Center of Cambodia has mapped 23,745 mass graves containing approximately 1.3 million suspected victims of execution. Direct execution is believed to account for up to 60% of the genocide's death toll,^[96] with other victims succumbing to starvation, exhaustion, or disease. The genocide triggered a second outflow of refugees, many of whom escaped to neighboring Thailand and, to a lesser extent, Vietnam.^[97]

In 2001, the Cambodian government established the Khmer Rouge Tribunal to try the members of the Khmer Rouge leadership responsible for the Cambodian genocide. Trials began in 2009, and in 2014, Nuon Chea and Khieu Samphan were convicted and received life sentences for crimes against humanity committed during the genocide.