Vietnam had been a French colony before it was occupied by the Japanese during World War Two.
After World War Two, it was returned to French control, but many Vietnamese people wanted independence.
As a result, in the 1950s, the French found themselves fighting a war against the Viet Minh, an organisation dedicated to getting rid of foreign imperialist powers from Vietnam.
Worried about the spread of communism in South East Asia, the USA began to financially support the French war effort in Vietnam.
In 1954, the French were finally defeated by the Viet Minh at the Battle of Dien Bien Phu.
This defeat was formalised in the Geneva Agreement.
The agreement temporarily separated Vietnam into two zones - a northern zone to be governed by the Viet Minh and a southern zone to be governed by an anti-communist government led by Ngo Dinh Diem.