The distant origins of the Vietnam War lie in the nineteenth-century colonisation of Indochina (Cambodia, Laos and Vietnam) by France. French rule lasted until 1940 when the Japanese, embarking on a series of conquests in Southeast Asia and eventually war against Western powers, occupied Vietnam. Japan's defeat in 1945 saw France seeking to regain control of her erstwhile colonies. Establishing the state of Vietnam, France installed the former emperor, Bao Dai, as head of state. For many Vietnamese, however, the end of the Japanese occupation meant the chance for independence, duly proclaimed by Ho Chi Minh, leader of Vietnam's Communist Party, in September 1945.
France refused to accept the declaration, and eight years of war followed, ending with the French defeat at Dien Bien Phu in 1954. The peace settlement, known as the Geneva Accords, divided the country; the North under the communist Ho Chi Minh, and the South under President Ngo Dinh Diem who had deposed Bao Dai and proclaimed the Republic of Vietnam in October 1955.
The Geneva Accords mandated that a Vietnam-wide election, aimed at reunifying the divided country, be held in 1956. Diem claimed that the people of the North could not vote freely, and with the backing of the United States, he refused to participate. Relations between the two Vietnams grew increasingly tense and in 1960 the North, aiming to overthrow Diem and reunite the country under communist rule, proclaimed the National Front for the Liberation of South Vietnam.
Known as the Viet Cong (Vietnamese Communists) and hoping to foment a general uprising, the Front embarked on a guerilla campaign throughout the South. The South Vietnamese Army proved unable to counter the insurgents' tactics and the United States, alarmed at the prospect of communism spreading throughout South-East Asia, began to significantly increase what had been a limited amount of assistance to the South. By 1962 more than 11,000 United States military advisers had arrived in the country. They represented the beginning of a build-up in United States troop numbers that would peak at more than 500,000.