Vietnam War

The Vietnam War (1 November 1955 – 30 April 1975) was an armed conflict in Vietnam, Laos, and Cambodia fought between North Vietnam (Democratic Republic of Vietnam) and South Vietnam (Republic of Vietnam) and their allies. North Vietnam was supported by the Soviet Union and China, while South Vietnam was supported by the United States and other anti-communist nations. The conflict was the second of the Indochina wars and a proxy war of the Cold War between the Soviet Union and US. The Vietnam War was one of the postcolonial wars of national liberation, a theater in the Cold War, and a civil war, with civil warfare a defining feature from the outset. Direct US military involvement escalated from 1965 until its withdrawal in 1973. The fighting spilled into the Laotian and Cambodian Civil Wars, which ended with all three countries becoming communist in 1975.

After the defeat of the French Union in the First Indochina War that began in 1946, Vietnam gained independence in the 1954 Geneva Conference but was divided in two at the 17th parallel: the Viet Minh, led by Ho Chi Minh, took control of North Vietnam, while the US assumed financial and military support for South Vietnam, led by Ngo Dinh Diem. The North Vietnamese supplied and directed the Viet Cong (VC), a common front of dissidents in the south which intensified a guerrilla war from 1957. In 1958, North Vietnam invaded Laos, establishing the Ho Chi Minh trail to supply the VC. By 1963, the north had covertly sent 40,000 soldiers of its People's Army of Vietnam (PAVN), armed with Soviet and Chinese weapons, to fight in the insurgency in the south. President John F. Kennedy increased US involvement from 900 military advisors in 1960 to 16,000 in 1963 and sent more aid to the Army of the Republic of Vietnam (ARVN), which failed to produce results. In 1963, Diem was killed in a US-backed military coup, which added to the south's instability.

Following the Gulf of Tonkin incident in 1964, the US Congress passed a resolution that gave President Lyndon B. Johnson authority to increase military presence without declaring war. Johnson launched a bombing campaign of the north and sent combat troops, dramatically increasing deployment to 184,000 by 1966, and 536,000 by 1969. US forces relied on air supremacy and overwhelming firepower to conduct search and destroy operations in rural areas. In 1968, North Vietnam launched the Tet Offensive, which was a tactical defeat but convinced many Americans the war could not be won. Johnson's successor, Richard Nixon, began "Vietnamization" from 1969, which saw the conflict fought by an expanded ARVN while US forces withdrew. The 1970 Cambodian coup d'état resulted in a PAVN invasion and US–ARVN counter-invasion, escalating its civil war. US troops had mostly withdrawn from Vietnam by 1972, and the 1973 Paris Peace Accords saw the rest leave. The accords were broken and fighting continued until the 1975 spring offensive and fall of Saigon to the PAVN, marking the war's end. North and South Vietnam were reunified in 1976.

The war exacted an enormous cost: estimates of Vietnamese soldiers and civilians killed range from 970,000 to 3 million. Some 275,000–310,000 Cambodians, 20,000–62,000 Laotians, and 58,220 US service members died. Its end would precipitate the Vietnamese boat people and the larger Indochina refugee crisis, which saw millions leave Indochina, of which about 250,000 perished at sea. 20% of South Vietnam's jungle was sprayed with toxic herbicides, which led to significant health problems.^{: 144–145} The Khmer Rouge carried out the Cambodian genocide, and the Cambodian–Vietnamese War began in 1978. In response, China invaded Vietnam, with border conflicts lasting until 1991. Within the US, the war gave rise to Vietnam syndrome, an aversion to American overseas military involvement, which, with the Watergate scandal, contributed to the crisis of confidence that affected America throughout the 1970s.