The Cambodian Civil War was a civil war in Cambodia fought between the forces of the Communist Party of Kampuchea against the government forces of the Kingdom of Cambodia and, after October 1970, the Khmer Republic, which had succeeded the kingdom.
The struggle was complicated by the influence and actions of the allies of the two warring sides. North Vietnam's People's Army of Vietnam involvement was designed to protect its Base Areas and sanctuaries in eastern Cambodia, without which the prosecution of its military effort in South Vietnam would have been more difficult. Their presence was at first tolerated by Prince Sihanouk, the Cambodian head of state, but domestic resistance combined with China and North Vietnam continuing to provide aid to the anti-government Khmer Rouge alarmed Sihanouk and caused him to go to Moscow to request the Soviets rein in the behavior of North Vietnam. The deposition of Sihanouk by the Cambodian National Assembly in March 1970, following wide scale protests in the capital against the presence of PAVN troops in the country, put a pro-American government in power which demanded that the PAVN leave Cambodia.