Vietnam War

War from 1954 to 1975 between communist North Vietnam and US-backed South Vietnam, in which North Vietnam aimed to conquer South Vietnam and unite the country as a communist state. North Vietnam was supported by communist rebels from South Vietnam, the Vietcong. The USA, in supporting the South against the North, aimed to prevent the spread of communism in Southeast Asia, but at the end of the war North and South Vietnam were reunited as a socialist republic.

Following the division of French Indochina into North and South Vietnam and the Vietnamese defeat of the French in 1954, US involvement in Southeast Asia grew through the Southeast Asia Treaty Organization (SEATO) pact. Non-communist South Vietnam was viewed, in the context of the 1950s and the Cold War, as a bulwark against the spread of communism throughout Southeast Asia. Advisers and military aid were dispatched to the region at increasing levels because of the so-called domino theory, which contended that the fall of South Vietnam would precipitate the collapse of neighbouring states. The USA spent $141 billion on aid to the South Vietnamese government, but corruption and inefficiency led the USA to assume ever greater responsibility for the war effort, until 1 million US combat troops were engaged.

In the USA, the draft, the high war casualties, the use of toxins such as napalm and Agent Orange, and the undeclared nature of the war resulted in growing domestic resistance, which caused social unrest and forced President Lyndon Johnson to abandon re-election plans. President Richard Nixon first expanded the war to Laos and Cambodia but finally phased out US involvement; his national security adviser Henry Kissinger negotiated a peace treaty in 1973 with North Vietnam, which soon conquered South Vietnam and united the nation.

Some 200,000 South Vietnamese soldiers, 1 million North Vietnamese soldiers, and 500,000 civilians were killed; 56,555 US soldiers were killed 1961–75. The war destroyed 50% of the country's forest cover and 20% of agricultural land. Cambodia, a neutral neighbour, was bombed by the USA 1969–75, with 1 million killed or wounded. Although US forces were never militarily defeated, Vietnam was considered a humiliating political defeat for the USA.