Nearly eight weeks before the 2 August 1964 Tonkin Gulf Incident, Lyndon Johnson made a statement to reporters at a press conference that the U.S. would defend South Vietnam against Northern aggression. According to John Prados, author of Vietnam: The History of an Unwinnable War, 1945-1975, this promise was a significant part of a series of decisions that contributed to the escalation of the war in Vietnam which can be traced back to the Eisenhower administration.

Much of the scholarship on the Vietnam War, according to Prados, was ‘atomized'—historians focused upon narrow aspects of the conflict, which then formed the basis for broader generalizations. Prados attempted to create a ‘unified theory' of the Vietnam War, by tracing U.S. actions from the end of World War II to the U.S. withdrawal from Saigon along a ‘commitment continuum.'

Following World War II, the U.S. had no commitments in Southeast Asia, and U.S. policy-makers had nearly limitless policy options in the region. Over the course of the next thirty years, however, as the U.S. commitment to Vietnam increased, this initially broad range of possibilities narrowed considerably.

Prados traced the beginnings of U.S. involvement in Vietnam back to the Eisenhower administration. Following the French defeat at Dien Bien Phu, Eisenhower felt that he had failed in his project to support the French in Vietnam, and consequently felt that he bore some responsibility for Vietnam's future. This, Prados posited, was what led the U.S. to support South Vietnamese President Ngo Dinh Diem in a bid to ensure the country's stability. Diem's failure to implement the democratic reforms demanded by the U.S. in turn led to his failure to secure popular support, and eventual overthrow and execution.

Having inherited Eisenhower's commitment to Vietnam, the Kennedy administration viewed South Vietnam as a convenient location for the U.S. to expand its influence in the region, experiment with covert operations and counter-insurgency tactics, and to demonstrate U.S. resolve in the Cold War. This perception of Vietnam as a low-consequence ‘sandbox' increased the United States' commitment and narrowed its flexibility to the point that by the time Lyndon Johnson assumed the presidency, it would have been nearly impossible for him to avoid an enlarged conflict.

In his assessment of Vietnam: The History of an Unwinnable War, 1945-1975, Thomas Hughes praised Prados' ‘unified theory' approach to the subject, but also pointed to several ‘situational factors' that motivated policy-makers but were not treated in the book. These included:

• false confidence prevalent among many Kennedy advisors that having successfully navigated the Cuban Missile Crisis, handling the Vietnamese would be comparatively easy
• The fact that during the height of the second Gulf of Tonkin incident on 4 August 1964, Johnson was also confronted with serious civil rights-related domestic political concerns. His tendency to handle Vietnam in the morning and civil-rights issues in the afternoon was, Hughes averred, "distracting."
• Finally, Hughes took issue with Prados' treatment of intelligence in the book which, according to Hughes, focused too much attention upon covert action, and consequently spent too little time dealing with traditional intelligence analysis of the type that the State Department's Bureau of Intelligence and Research was engaged in.

One of the main themes that pervaded the U.S. involvement in Vietnam, according to Larry Berman, was a lack of understanding of Vietnamese nationalism. Had the U.S. not become involved following Dien Bien Phu, Vietnam likely would have recovered and reunified. Because U.S. involvement came so quickly on the heels of the French exit, however, many Vietnamese saw the U.S. as a colonial replacement for the French.

Taking issue with Prados, however, and explaining what he called the "you break it you buy it" approach to international relations, Berman felt that until the Kennedy Administration turned a blind eye to (and even tacitly supported) the overthrow and execution of President Ngo Dinh Diem in 1963, the United States could have avoided further escalation of its involvement in the country.

Finally, Berman said that there were some in the U.S. administration who believed that if you removed American financial support then the South Vietnamese leadership would simply stop doing the things that the U.S. wanted them to do. This attitude towards these supposed allies was troubling to Berman, and helped to explain the reason why the U.S. never achieved broad, wide-spread support among the South Vietnamese citizenry.