The United States entered the War to prevent a Communist takeover of South Vietnam as part of their wider strategy of commitment. Military advisors arrived beginning in 1950. US involvement escalated in early 1960s, with US troop levels trippling in 1961 and trippling 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. After this, US ground forces, were withdrawn as part of a policy called Vietnamization. Despite the Paris Peace accords, signed by all parties in January 1973, fighting continued.
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 US  soldiers.

Various names have been applied to the conflict . Vietnam War is the most commonly used name in English. It has also been called the Second Indochina War, and the Vietnam Conflict.

The main military organizations involved in the War were, on one side, the Army of the Republic of Vietnam and the US military, on the other hand, the Vietnam People's army or North Vietnamese Army and the Vietcong, or National Front  for the Liberation of South Vietnam, a south Vietnamese communist army.