Cambodian Civil War

The Cambodian Civil War (Khmer: សង្គ្រាមស៊ីវិលកម្ពុជា, UNGEGN: Sângkréam Sivĭl Kâmpŭchéa) was a civil war in Cambodia fought between the Communist Party of Kampuchea (known as the Khmer Rouge, supported by North Vietnam and China) against the government of the Kingdom of Cambodia and, after October 1970, the Khmer Republic, which had succeeded the kingdom after a coup (both supported by the United States and South Vietnam). The conflict was part of the Second Indochina War (1955–1975).

The conflict was linked to the Vietnam War. The North Vietnamese People's Army of Vietnam (PAVN) was involved to protect its bases in eastern Cambodia, which were crucial to its military effort in South Vietnam. This presence was initially tolerated by Prince Sihanouk, the Cambodian head of state, but domestic resistance combined with China and North Vietnam aiding the anti-government Khmer Rouge caused him to request help from the Soviet Union to stop this.

In March 1970, Sihanouk was deposed by the Cambodian National Assembly, following wide scale protests in the capital against the PAVN presence in the country. He was replaced by a pro-American government which demanded that the PAVN leave Cambodia. They refused and, at the request of the Khmer Rouge, invaded Cambodia, capturing most of the northeastern third of the country from the Khmer National Armed Forces (FANK) between March and June 1970. They handed over some of the territory to the Khmer Rouge and increased material assistance to the group, thus empowering what was at the time a small guerrilla movement. In response, FANK was expanded to fight the PAVN and growing Khmer Rouge. U.S. involvement was motivated by the desire to buy time for its withdrawal from Southeast Asia, to protect South Vietnam, and to prevent the spread of communism to Cambodia. The U.S. assisted the Khmer government with massive U.S. aerial bombing campaigns and direct material and financial aid, while the PAVN continued to occupy Cambodian territory and occasionally engage the FANK in combat.

On 17 April 1975, after five years of fighting, the Khmer Republic was ultimately defeated, with the victorious Khmer Rouge proclaiming the establishment of Democratic Kampuchea. The war caused a refugee crisis in Cambodia with two million people—more than 25 percent of the population—displaced from rural areas into the cities, with the capital Phnom Penh's population growing from 600,000 in 1970 to nearly 2 million by 1975. Children were frequently persuaded or forced to commit atrocities during the war. The Cambodian government estimated that more than 20 percent of the property in the country had been destroyed during the war. In total, an estimated 275,000–310,000 people were killed as a result of the war, including 30,000 to 150,000 killed in U.S. bombing campaigns. Once in power, the Khmer Rouge carried out the Cambodian genocide, one of the deadliest in history.