War dominated 30 years of Vietnam's history last century. The struggle that began with communists fighting French colonial power in the 1940s did not end until they seized Saigon and control of the whole country in 1975.
The period that Americans refer to as the "Vietnam War" – and the Vietnamese call the "American War" – was the US military intervention from 1965 to 1973.
Communist forces based in the north and led by the nationalist leader Ho Chi Minh defeated the French in 1954.
Accords were negotiated that split the country into communist north and pro-American south, divided by a demilitarised zone (DMZ).
Country-wide elections to decide a permanent solution were promised but never happened, and within five years the communists had launched a guerrilla war on the south.
Hundreds of thousands of US soldiers were sent to help fight the communists in a costly and ultimately unsuccessful war which brought domestic civil unrest and international embarrassment.
The US was driven by Cold War concerns about the spread of communism, particularly "domino theory" – the idea that if one Asian nation fell to the leftist ideology, others would quickly follow.
The Vietnam War was protracted and bloody. The Hanoi government estimates that in 21 years of fighting, four million civilians were killed across North and South Vietnam, and 1.1 million communist fighters died.
US figures covering the American phase record 200-250,000 South Vietnamese soldiers killed and 58,200 US soldiers dead or missing in action.