The Vietnam War (Vietnamese: Chiến tranh Việt Nam), also known as the Second Indochina War, and in Vietnam as the Resistance War Against America (Vietnamese: Kháng chiến chống Mỹ) or simply the American War, was a conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975, with U.S. involvement ending in 1973. It was the second of the Indochina Wars and was officially fought between North Vietnam and the government of South Vietnam. The North Vietnamese army was supported by the Soviet Union, China, and other communist allies; the South Vietnamese army was supported by the United States, South Korea, the Philippines, Australia, Thailand and other anti-communist allies. The war is considered a Cold War-era proxy war by some US perspectives. The war would last approximately 19 years and would also form the Laotian Civil War as well as the Cambodian Civil War, which resulted in all three countries becoming communist states in 1975.
Beginning in 1950, American military advisors arrived in what was then French Indochina. Most of the funding for the French war effort was provided by the U.S. The Việt Cộng, also known as Front national de libération du Sud-Viêt Nam or NLF (the National Liberation Front), a South Vietnamese communist common front aided by the North, fought a guerrilla war against anti-communist forces in the region, while the People's Army of Vietnam (PAVN), also known as the North Vietnamese Army (NVA), engaged in more conventional warfare, and had launched armed struggles from 1959 onward. U.S. involvement escalated in 1960 under President John F. Kennedy, with troop levels gradually surging under the MAAG program from just under a thousand in 1959 to 16,000 in 1963.
By 1964 there were 23,000 U.S. troops in Vietnam, but this escalated further following the 1964 Gulf of Tonkin incident, in which a U.S. destroyer was alleged to have clashed with North Vietnamese fast attack craft. In response, the Gulf of Tonkin Resolution gave President Lyndon B. Johnson broad authorization to increase U.S. military presence, deploying ground combat units for the first time and increasing troop levels to 184,000. Every year onward there was significant build-up despite little progress, with Robert McNamara, one of the principal architects of the war, beginning to express doubts of victory by the end of 1966. U.S. and South Vietnamese forces relied on air superiority and overwhelming firepower to conduct search and destroy operations, involving ground forces, artillery, and airstrikes. The U.S. conducted a large-scale strategic bombing campaign against North Vietnam. After the Tet Offensive of 1968, the Army of the Republic of Vietnam (ARVN) unconventional and conventional capabilities increased following a period of neglect and became modeled on heavy fire-power focused doctrines like US forces. Operations crossed international borders: bordering areas of Laos and Cambodia were used by North Vietnam as supply routes and were heavily bombed by U.S. forces.
Gradual withdrawal of U.S. ground forces began as part of "Vietnamization", which aimed to end American involvement in the war while transferring the task of fighting the communists to the South Vietnamese themselves and began the task of modernizing their armed forces. Direct U.S. military involvement ended on 15 August 1973 as a result of the Case–Church Amendment passed by the U.S. Congress. The capture of Saigon by the PAVN in April 1975 marked the end of the war, and North and South Vietnam were reunified the following year. The war exacted a huge human cost in terms of fatalities (see Vietnam War casualties). Estimates of the number of Vietnamese soldiers and civilians killed vary from 966,000 to 3.8 million. Some 275,000–310,000 Cambodians, 20,000–62,000 Laotians, and 58,220 U.S. service members also died in the conflict, and a further 1,626 remain missing in action. The Sino-Soviet split re-emerged following the lull during the Vietnam War and ties between the DRV and its Cambodian allies in the Royal Government of the National Union of Kampuchea, the newly-formed Democratic Kampuchea begun almost immediately in a series of border raids by the Khmer Rouge and erupted into the Cambodian–Vietnamese War, with Chinese forces directly intervening in the Sino-Vietnamese War. The end of the war and resumption of the Third Indochina War would precipitate the Vietnamese boat people and the bigger Indochina refugee crisis, which saw an estimated 250,000 people perish at sea.