The United States took part in the Vietnam War to prevent communist takeover of South Vietnam.
Indochina Wars . The Second Indochina War ( called the Vietnam War in the West or the American War in Vietnam ) began as a conflict between the United States-backed South Vietnamese government and its opponents , both the North Vietnamese-based communist Viet Cong ( National Liberation Front ) and the People 's Army of Vietnam ( PAVN ) , known in the West as the North Vietnamese Army ( NVA ) . The conflict began in the late 1950s and lasted until 1975 when the North Vietnamese conquered South Vietnam . Vietnam War . The North Vietnamese army was supported by the Soviet Union , China and other communist allies and the South Vietnamese army was supported by the United States , South Korea , Australia , Thailand and other anti-communist allies . The U.S. government viewed its involvement in the war as a way to prevent a communist takeover of South Vietnam .