American foreign policy after World War II had been based on the goal of containing Communism and the assumptions of the so-called "domino theory”—that if one country fell to Communism, the surrounding countries would fall, like dominoes. The Eisenhower administration was concerned that if Vietnam fell under Communist control, other Southeast Asian and Pacific nations, including even the Philippines, would fall one by one. In response to that threat, the Southeast Asia Treaty Organization (SEATO) was formed in 1955 to prevent Communist expansion. President Eisenhower sent some 700 military personnel as well military and economic aid to the government of South Vietnam. This effort was foundering when John F. Kennedy became president.
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