The Second Indochina War, known in the USA as the Vietnam War, was a Cold War era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975.

The war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of South Vietnam, supported by the US. and other anti-communist nations. The US government viewed involvement in the war as a way to prevent a communist takeover of South Vietnam and part of their wider strategy of containment. The North Vietnamese government viewed the war as a colonial war, fought initially against France, backed by the US, and later against South Vietnam, which it regarded as a US puppet state.

US military advisers arrived beginning in 1950. US involvement escalated in the early 1960s, with troop levels tripling in 1961 and tripling again in 1962. US combat units were deployed beginning in 1965. Operations spanned borders, with Laos and Cambodia heavily bombed. Involvement peaked in 1968 at the time of the Tet Offensive.

US military involvement ended on 15 August 1973. The capture of Saigon by the North Vietnamese army in April 1975 marked the end of the Vietnam War with a Communist victory.