The Vietnam saga began during the Second World War, when Vietnamese guerrillas fighting Japanese occupation of Indochina worked with American and British forces in the effort at forcing the Japanese out of the region. The leader of the Vietnamese resistance was Ho Chi Minh, a communist dedicated to permanently ousting all foreign troops and establishing a socialist bastion across Southeast Asia. With the Japanese defeat, Ho became the first prime minister of an independent Vietnam.
While Ho began to establish the Democratic Republic of Vietnam, British forces, occupying Saigon in the southern half of the country, relinquished its control to the region's pre-war colonial power, France. France desired to reconstitute its old colonial empire in what was called French Indochina. Recognizing the political developments underway in Vietnam, the French concluded an agreement with the Vietnamese that ostensibly provided for a "free state" within the French Union. French determination to reestablish its sovereignty over Vietnam, however, soon conflicted with the determination of the Vietnamese to unify their country under an independent flag while spreading its influence to neighboring Laos and Cambodia, also French colonial holdings. In 1946, the French-Vietminh war erupted.
During the late 1940s, the United States was preoccupied with the emerging Cold War with the Soviet Union, and was attempting to establish a alliance uniting West European countries liberated from German occupation to defend against the perceived threat of aggression from the Soviet Army occupying Eastern Europe and the eastern half of Germany. French intransigence in the U.S.-led negotiations over what would become the North Atlantic Alliance resulted in a quid pro quo agreement between Washington and Paris in which the former would support French territorial ambitions in Southeast Asia in exchange for French support for and participation in the new western alliance. The United States subsequently initiated material support for the French Army in its efforts at defeating the Vietminh. In 1950, the Soviet and Chinese initiated military support for Ho Chi Minh's forces -- support that would continue for the next quarter-century.
In 1953, France granted Laos independence, providing an opportunity for the Vietminh to make inroads there. Nineteen-fiftyfour would be a watershed year in the region's history, as the Vietminh defeated the French at Dien Bien Phu. Multinational negotiations ensued regarding Vietnam's future resulting in the Geneva Accords in which the country was divided along the 17th Parallel, a result soon rejected by the United States and the nascent government in the south. The South Vietnamese leader, Ngo Dinh Diem, refused to cooperate. By 1956, the United States began its training program for the south's military, dubbed the U.S. Military Assistance Advisory Group, and the U.S. role in Vietnam, in the south, supplanted that of the French. Ho began a program of infiltrating large numbers of guerrillas into the south, supporting them through the development of the "Ho Chi Minh trail," running through Laos, Cambodia, and into South Vietnam. From 1960 to 1965, the American presence and role in Vietnam would grow. In 1961, President Kennedy authorized U.S. Special Forces to assist the south. His support for Diem's overthrow further destabilized the country. His assassination saw his replacement, Lyndon Johnson, escalate U.S. participation.