The Cambodian genocide was the campaign of mass killing carried out by the Khmer Rouge regime of Pol Pot between April 17, 1975, when the Khmer Rouge took Phnom Penh, and January 7, 1979, when the Vietnamese captured the city and ended the regime. In less than four years, an estimated 1.5 to 2 million Cambodians — roughly a quarter of the country’s 1975 population of 7.9 million — were killed through execution, forced labor, starvation, and disease. The Cambodian genocide is, after the Holocaust and the Rwandan genocide, the most thoroughly documented case of state-organized mass killing in the twentieth century — the one in which the percentage of the population destroyed was the highest.
The genocide proceeded in three overlapping phases. The first, April 17, 1975 – late 1976, was the forced evacuation of the cities. The Khmer Rouge marched the entire population of Phnom Penh — roughly 2 million people — and the populations of Battambang, Siem Reap, Kompong Cham, and other cities into the countryside, with no notice, in conditions of extreme heat. The evacuation was carried out under the slogan “the people have the rice” (prachea mean bon), and the rationale was that the new society required a rural labor force to build agricultural cooperatives. The death toll in the first weeks alone is estimated at 100,000 to 200,000, mostly from disease, hunger, and exhaustion in the forced marches.
The second phase, 1976 – mid 1978, was the establishment of the cooperatives and the targeting of the “new people” (khon santehanak). The population was divided into “base people” (khon chamkar) — the rural majority, who were treated as revolutionary subjects — and the “new people,” the urban evacuees, who were treated as class enemies. The cooperatives were organized as forced labor camps with inadequate food, no medical care, and routine execution for minor infractions. The killing was concentrated against the educated: former government officials, military officers, teachers, students, Buddhist monks, ethnic Chinese, ethnic Vietnamese, the Cham Muslim minority, and any speaker of French. The Tuol Svay Prey High School in Phnom Penh, renamed S-21 and run by the regime’s internal security chief Kang Kek Iew (later Comrade Duch), processed at least 14,000 prisoners, of whom perhaps five survived. Choeung Ek, one of several “killing fields” outside the capital, holds the remains of an estimated 20,000 victims.
The third phase, mid 1977 – January 1979, was the purge of the Khmer Rouge’s own cadre and the border wars. The regime’s own Central Committee, which had governed Cambodia since 1963, was almost entirely eliminated. By the time of the Vietnamese invasion, Nuon Chea (Brother Number Two), Son Sen (the Minister of Defense), and Ieng Sary (the Foreign Minister) had all been targeted; the survivors were few. The border wars with Vietnam, which began in April 1977 and intensified through 1978, killed several thousand Vietnamese civilians and produced the political context for the Vietnamese invasion of December 25, 1978.
The genocide ended with the Vietnamese invasion. The fall of Phnom Penh on January 7, 1979, the establishment of the People’s Republic of Kampuchea under the Khmer defectors Heng Samrin and Hun Sen, and the flight of the surviving Khmer Rouge leadership to the Thai border ended the killing fields. The survivors of the regime, perhaps 1.5 million in mid-1979, faced a famine in 1979–1980 that killed an additional 500,000 to 1,000,000 — a number that is sometimes included in the genocide’s death toll, and sometimes counted separately.
The standard scholarly account is Ben Kiernan’s The Pol Pot Regime (1996, 2008), based on a decade of interviews with survivors, defectors, and former cadre. Other major sources include the Tuol Sleng Genocide Museum Archives in Phnom Penh (1979–), the Documentation Center of Cambodia (Phnom Penh, established 1995), and the Extraordinary Chambers in the Courts of Cambodia trial record (2007–2022). The ECCC convicted three senior Khmer Rouge leaders — Comrade Duch in 2010, Nuon Chea and Khieu Samphan in 2018 — of genocide and crimes against humanity. For more on the Cambodian-Vietnamese War article.