The Cambodian Civil War is a conflict that pits the forces of the Communist Party of Kampuchea (known as the Khmer Rouge) and their allies the Democratic Republic of Vietnam (North Vietnam) and the National Front for the Liberation of South Vietnam (NLF, or, Viet Cong) against the government forces of Cambodia (after October 1970, the Khmer Republic), which are supported by the United States (U.S.) and the Republic of Vietnam (South Vietnam).The struggle is exacerbated by the influence and actions of the allies of the two warring sides.

North Vietnamese Army involvement is designed to protect its Base Areas and sanctuaries in eastern Cambodia, without which the prosecution of its military effort in South Vietnam would be more difficult.

The U.S. is motivated by the need to buy time for its withdrawal from Southeast Asia and to protect its ally, South Vietnam.

American, South and North Vietnamese forces directly participate (at one time or another) in the fighting.

The central government is mainly assisted by the application of massive U.S. aerial bombing campaigns and direct material and financial aid.After five years of savage fighting that bring about massive casualties, the destruction of the economy, the starvation of the population, and grievous atrocities, the Republican government is defeated on April 17, 1975 when the victorious Khmer Rouge proclaim the establishment of Democratic Kampuchea.

This conflict, although an indigenous civil war, is considered to be part of the larger Second Indochina War (1960–1975) that also consumei the neighboring Kingdom of Laos, South Vietnam, and North Vietnam.