The Vietnam War (Vietnamese: Chien tranh viet Nam) also known as the Second Indochina War,and in Vietnam as the Resistance War Against America (Vietnamese: Khangchien chong My) or simply the American 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 was officially fought between North Vietnam and South Vietnam. North Vietnam was supported by the Soviet Union, China,and other communist allies; South Vietnam was supported by the United States, South Korea, the Philippines, Australia, Thailand, and other anti-communist allies. The war, considered a Cold War-era proxy war by some, lasted 19 years, with direct U.S. involvement ending in 1973, and included the Laotian Civil War and the Cambodian Civil War, which ended with all three countries becoming communist in 1975.
The conflict emerged from the First Indochina War against the communist-led Viet Minh.Most of the funding for the French war effort was provided by the U.S. After the French quit Indochina in 1954, the US assumed financial and military support for the South Vietnamese state. The Viet cong, also known as Front national de liberation du Sud-Viet Nam or NLF (the National Liberation Front), a South Vietnamese common front under the direction of North Vietnam, initiated a guerrilla war in the south. North Vietnam had also invaded Laos in the mid-1950s in support of insurgents, establishing the Ho Chi Minh Trail to supply and reinforce the Viet Cong 16 U.S. involvement escalated under President John F. Kennedy through the MAAG program from just under a thousand military advisors in 1959 to 16,000 in 131 By 1963, the North Vietnamese had sent 40,000 soldiers to fight in South Vietnam.16 North Vietnam was heavily backed by the USSR and the People's Republic of China. China also sent hundreds of PLA servicemen to North Vietnam to serve in air-defense and support roles.
By 1964, 23,000 US advisors were stationed in South Vietnam. In the Gulf of Tonkin incident in August, a U.S. destroyer was alleged to have clashed with North Vietnamese fast attack craft. In response, the U.S. Congress passed the Gulf of Tonkin Resolution and gave President Lyndon B. Johnson broad authority to increase American military presence in Vietnam. Johnson ordered the deployment of combat units for the first time and increased troop levels to 184,000. Past this point, the People's Army of Vietnam (PAVN) (also known as the North Vietnamese Army or NVA) engaged in more conventional warfare with U.S and South Vietnamese forces. Despite little progress, the United States continued a significant built-up of forces. U.S. Secretary of Defense Robert McNamara, one of the principal architects of the war, began expressing doubts of victory by the end of 1966.287 U.S. and South Vietnam forces relied on air superiority and overwhelming firepower to conduct search and destroy operations, involving ground forces, artillery, and airstrikes. The U.S. also conducted a large-scale strategic bombing campaign against North Vietnam and Laos.
The Tet Offensive of 1968 showed the lack of progress with these doctrines. With the VC and PAVN mounting large-scale urban offensives throughout 1968, U.S domestic support for the war began fading. The Army of the Republic of Vietnam (ARVN) expanded following a period of neglect after Tet and was modeled after U.S doctrine. The VC sustained heavy losses during the Tet Offensive and subsequent U.S.-ARVN operations in the rest of 1968, losing over 50,000 men.481 The CIA's Phoenix Program further degraded the VC's membership and capabilities. By the end of the year, the VC insurgents held almost no territory in South Vietnam, and their recruitment dropped by over 80% in 1969, signifying a drastic reduction in guerrilla operations, necessitating increased use of PAVN regular soldiers from the north.247–9 In 1969, North Vietnam declared a Provisional Revolutionary Government in South Vietnam in an attempt to give the reduced VC a more international stature, but the southern guerrillas from then on were sidelined as PAVN forces began more conventional combined arms warfare. By 1970, over 70% of communist troops in the south were northerners, and southern-dominated VC units no longer existed.Operations crossed national borders: Laos was invaded by North Vietnam early on, while Cambodia was used by North Vietnam as a supply route starting in 1967; the route through Cambodia began to be bombed by the U.S. in 1969, while the Laos route had been heavily bombed since 1964. The deposing of the monarch Norodom Sihanouk by the Cambodian National Assembly resulted in a PAVN invasion of the country at the request of the Khmer Rouge, escalating the Cambodian Civil War and resulting in a U.S.-ARVN counter-invasion.
In 1969, following the election of U.S President Richard Nixon, a policy of "Vietnamization" began, which saw the conflict fought by an expanded ARVN with U.S. forces sidelined and increasingly demoralized by domestic opposition and reduced recruitment. U.S. ground forces had largely withdrawn by early 1972 and support was limited to air support, artillery support, advisers, and materiel shipments. The ARVN, buttressed by said U.S. support, stopped the first and largest mechanized PAVN offensive during the Easter Offensive of 1972. The offensive resulted in heavy casualties on both sides and the failure of the PAVN to subdue South Vietnam, but the ARVN itself failed to recapture all territory, leaving its military situation difficult. The Paris Peace Accords of January 1973 saw all U.S forces withdrawn; the Case–Church Amendment, passed by the U.S Congress on 15 August 1973, officially ended direct U.S military involvement.