During World War II, Japan occupied French-held regions in Asia (commonly called Indochina). As well as fighting the French, the Viet Minh started a campaign against the Japanese. Due to their opposition to the Japanese, the Viet Minh received funding from the Americans and the Chinese. When Japan surrendered in August 1945, the Viet Minh tried to take control of the country and declared independence from France. The declaration of independence was followed by nearly ten years of war against France, with France's effort largely funded by the United States.
The French surrendered in 1954 following the Battle of Dien Bien Phu. Shortly thereafter, as a result of peace accords worked out in Geneva, Switzerland, Vietnam was divided into North Vietnam and South Vietnam, ostensibly only as a temporary measure until unifying elections would take place in 1956. The Viet Minh took control of North Vietnam on October 11, 1954. Ho Chi Minh was appointed Prime Minister of North Vietnam, which became a communist state.
South Vietnam and its chief supporter, the United States, reneged on the 1954 agreement and refused to hold unifying elections, fearing that Ho Chi Minh was seen as a national hero and would thus win the elections. As a result, guerillas in South Vietnam (including many ex-Viet Minh) who opposed the anti-communist regime there united to form the National Front for the Liberation of Vietnam, called Viet Cong by the Americans and South Vietnamese.