Source: U.S. Department of Defense, Special Report on American Commitment to Vietnam
U.S. Department of Defense, United States-Vietnamese Relations 1945-1967 (Washington, D.C.: House Committee on Armed Services, 1971), Book 2 (IV.B.1.), pp. 67.
Finally, in this review of factors that would affect policy-making in Vietnam, we must note that South Vietnam (unlike any of the other countries in Southeast Asia) was essentially the creation of the United States.
Without U.S. support Diem almost certainly could not have consolidated his hold on the South during 1955 and 1956.
Without the threat of U.S. intervention, South Vietnam could not have refused to even discuss the elections called for in 1956 under the Geneva settlement without being immediately overrun by the Viet Minh armies.
Without U.S. aid in the years following, the Diem regime certainly, and an independent South Vietnam almost as certainly, could not have survived.