Diem's brother, Ngo Dinh Nhu, had raided the Buddhist pagodas of South Vietnam, claiming that they had harbored the Communists that were creating the political instability. The result was massive protests on the streets of Saigon that led Buddhist monks to self-immolation. The pictures of the monks engulfed in flames made world headlines and caused considerable consternation in Washington. By late September, the Buddhist protest had created such dislocation in the south that the Kennedy administration supported a coup. In 1963, some of Diem's own generals in the Army of the Republic of Vietnam (ARVN) approached the American Embassy in Saigon with plans to overthrow Diem. With Washington's tacit approval, on November 1, 1963, Diem and his brother were captured and later killed. Three weeks later, President Kennedy was assassinated on the streets of Dallas.

At the time of the Kennedy and Diem assassinations, there were 16,000 military advisers in Vietnam. The Kennedy administration had managed to run the war from Washington without the large-scale introduction of American combat troops. The continuing political problems in Saigon, however, convinced the new president, Lyndon Baines Johnson, that more aggressive action was needed. Perhaps Johnson was more prone to military intervention or maybe events in Vietnam had forced the president's hand to more direct action. In any event, after a dubious DRV raid on two U.S. ships in the Gulf of Tonkin, the Johnson administration argued for expansive war powers for the president.