The Vietnam War was a conflict in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. It was the second of the Indochina Wars and was a major conflict of the Cold War. While the war was officially fought between North Vietnam and South Vietnam, the north was supported by the Soviet Union, China, and other communist states, while the south was supported by the United States and other anti-communist allies, making the war a proxy war between the United States and the Soviet Union. It lasted almost 20 years, with direct U.S. military involvement ending in 1973. The conflict also spilled over into neighboring states, exacerbating the Laotian Civil War and the Cambodian Civil War, which ended with all three countries officially becoming communist states by 1976.

The Khmer Rouge is the name that was popularly given to members of the Communist Party of Kampuchea (CPK) and by extension to the regime through which the CPK ruled Cambodia between 1975 and 1979. The name was coined in the 1960s by then Chief of State Norodom Sihanouk to describe his country's heterogeneous, communist-led dissidents, with whom he allied after his 1970 overthrow.