The conflict emerged from the First Indochina War against the communist-led Viet Minh.[A 4] 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 Việt Cộng, also known as Front national de libération du Sud-Viêt 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 entered Laos in the mid-1950s in support of insurgents, setting up the Ho Chi Minh trail to supply and reinforce the Việt Cộng and increased in 1960. U.S. involvement escalated under President John F. Kennedy through the MAAG program from just under a thousand in 1959 to 16,000 in 1963. By 1963, the North Vietnamese had sent 40,000 soldiers to fight in South Vietnam. North Vietnam was heavily backed by the People's Republic of China, which in addition to supplying arms as the USSR did, also sent hundreds of thousands of PLA servicemen to North Vietnam to serve in support roles.
The Tet Offensive of 1968 showed the lack of progress with these doctrines as the NLF and PAVN mounted large-scale urban offensives throughout 1968, turning US domestic support against the war. The Army of the Republic of Vietnam (ARVN) expanded following a period of neglect after Tet, modeled on US doctrine. The NLF sustained heavy losses during the Tet Offensive, losing over half its strength in a matter of months, which combined with subsequent U.S.-ARVN operations in the rest of 1968, nearly wiped out the southern insurgency. The CIA's Phoenix Program further degraded the NLF's membership and capabilities. By the end of the year, the NLF insurgents held almost no territory in South Vietnam, and their recruitment dropped by over 80% in 1969, signifying a drastic reduction in guerrilla operations and necessitating increased use of NVA regulars from the north. In 1969, North Vietnam declared a Provisional Revolutionary Government in South Vietnam in an attempt to give the reduced NLF a more international stature, but the southern guerrillas from then on were sidelined as PAVN forces begun more conventional Combined arms warfare. 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 deposition 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.-RVN counterinvasion.
After 1968, Nixon's policy of "Vietnamization", 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 withdrew by late 1971, and U.S. involvement became limited to air support, artillery support, advisers, and materiel shipments. The ARVN, buttressed by said U.S. support, stopped the largest and first mechanized PAVN offensive to date during the Easter Offensive of 1972, resulting in mutually heavy casualties, but failed to recapture all territory, leaving its military situation difficult. The Paris Peace Accords saw all US forces withdrawn and intervention prohibited by the US Congress on 15 August 1973 as a result of the Case–Church Amendment. The Peace Accords were broken almost immediately, and fighting continued for four years following the withdrawal of U.S. ground forces and two years following the withdrawal of the remaining U.S. forces, though U.S. material support continued at a much reduced rate. The three-year period of 1972 to 1974 saw heavy fighting and constituted the war's bloodiest years for the ARVN. The 1975 Spring Offensive culminated in the capture of Saigon by the PAVN in April 1975; this marked the end of the war, and North and South Vietnam were reunified the following year.
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.
Given that there have been several conflicts in Indochina, this particular conflict is known by the names of its primary protagonists, in order to distinguish it from others. In Vietnamese, the war is generally known as Kháng chiến chống Mỹ (Resistance War Against America), but less formally as 'Cuộc chiến tranh Mỹ' (The American War). It is also called Chiến tranh Việt Nam (The Vietnam War).