The Vietnam War, also known as the Second Indochina War, the Vietnam Conflict, or often in Vietnam, the American War occurred in Vietnam, Laos and Cambodia from 1955 to April 30, 1975. The war was fought between the communist North Vietnam, supported by its communist allies, and the government of South Vietnam, supported by the United States and other member nations of the Southeast Asia Treaty Organization (SEATO).

The Vietcong, the lightly armed South Vietnamese communist insurgency, largely fought a guerrilla war against anti-communist forces in the region. The North Vietnamese Army engaged in a more conventional war, at times committing large-sized units into battle. U.S. and South Vietnamese forces relied on air superiority and overwhelming firepower to conduct search-and-destroy operations, involving ground forces, artillery and air strikes.

The United States entered the war to prevent a communist takeover of South Vietnam as part of their wider strategy of containment. Military advisors arrived beginning in 1950. U.S. involvement escalated in the early 1960s and combat units were deployed beginning in 1965. Involvement peaked in 1968 at the time of the Tet Offensive. Despite a peace treaty signed by all parties in January 1973, fighting continued. In April 1975, North Vietnam captured Saigon. North and South Vietnam were reunified the following year.

The war exacted a huge human cost in terms of fatalities, including 3 to 4 million Vietnamese from both sides, 1.5 to 2 million Laotians and Cambodians, and 58,159 U.S. soldiers.