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Why did President John F. Kennedy increase U.S. aid to South Vietnam?

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Vietnam War U.S. troops wading through a marsh in the Mekong delta, South Vietnam, 1967.

President John F. Kennedy increased U.S. aid to South Vietnam primarily to test the American capacity for counterinsurgency and to demonstrate a firm commitment to halting communist expansion.1

Kennedy viewed the Viet Cong’s struggle against the government of Ngo Dinh Diem as a prime example of communist-led "wars of national liberation" supported by China and the Soviet Union. Guided by the domino theory—which posited that the fall of one Southeast Asian nation would lead to the collapse of others—Kennedy considered South Vietnam the "cornerstone of the free world" in the region.12

Following assessments by advisers Walt W. Rostow and Maxwell Taylor, which concluded that the South Vietnamese government could not survive on its own, Kennedy expanded military assistance to include technical experts, helicopters, and armoured personnel carriers. Ultimately, he sought to avoid the domestic political consequences of "losing" a country to communism while remaining reluctant to commit U.S. combat troops.12