Final answer:
The U.S. fought in Vietnam primarily to oppose the spread of communism during the Cold War, supporting South Vietnam against North Vietnamese communists. The conflict, initially rooted in colonial liberation, evolved into a proxy war as part of the larger effort to contain communist influence globally. The U.S. military commitment increased under President Johnson to prevent a 'domino effect' in Southeast Asia.
Step-by-step explanation:
Primary Reason the U.S. Fought in Vietnam
The primary reason the United States fought in Vietnam was to oppose the spread of communism. Initially, during and after World War II, the U.S. had supported the Viet Minh, who were also fighting against the Japanese. The Viet Minh, led by H_o Chi Minh, were a nationalist group seeking Vietnamese independence, which they declared following Japan's surrender. However, when the Viet Minh, led by communist H_o Chi Minh, attempted to prevent French reassertion over Vietnam after World War II, the U.S chose to back France, an important Western ally, thus ending its support for H_o Chi Minh.
French Indochina, which included Vietnam, had been a colony of France from the late 1800s until Japan seized control during World War II. After the war, the French aimed to reestablish their colonial rule, but faced strong resistance from the Viet Minh. Despite H_o Chi Minh's interest in American principles of self-determination, the U.S. decided to support France as part of its larger strategy to contain communism worldwide, especially during the Cold War. This support continued after the defeat of France, with the United States increasingly committing military resources to support South Vietnam against the North Vietnamese communists.
As the conflict escalated, President Lyndon Johnson decided to increase military involvement to prevent a potential domino effect, fearing that if Vietnam fell to communism, other countries in the region might do the same. By 1965, a significant number of U.S. troops were present in Vietnam, which led to domestic strife within the U.S. over the war's merits and objectives. Simultaneously, the Soviet Union supported H_o Chi Minh's regime, turning the Vietnam conflict into a proxy war between the superpowers.