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 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 US and anti-communist allies. This made it a proxy war between the US and Soviet Union. It lasted almost 20 years, with direct US military involvement ending in 1973. The conflict spilled into the Laotian and Cambodian civil wars, which ended with all three countries becoming communist in 1975.

After the fall of French Indochina with the 1954 Geneva Conference, the country gained independence from France but was divided into two parts: the Viet Minh took control of North Vietnam, while the US assumed financial and military support for South Vietnam. The Viet Cong (VC), a South Vietnamese common front under the direction of the north, initiated guerrilla war in the south. The People's Army of Vietnam (PAVN) engaged in more conventional warfare with US and Army of the Republic of Vietnam (ARVN) forces. North Vietnam invaded Laos in 1958, establishing the Ho Chi Minh trail to supply and reinforce the VC.^: 16 By 1963, the north had sent 40,000 soldiers to fight in the south.^: 16 US involvement increased under President John F. Kennedy, from 1,000 military advisors in 1959 to 23,000 by 1964.^: 131

Following the Gulf of Tonkin incident in 1964, the US Congress passed a resolution that gave President Johnson authority to increase military presence, without a declaration of war.