Which of the following presidents approved the backing of the South Vietnamese in their Civil War?

President Lyndon B. Johnson is the one who significantly escalated U.S. involvement in the Vietnam War by approving military support for South Vietnam during its civil conflict against the North. Although earlier presidents, such as Dwight D. Eisenhower and John F. Kennedy, also provided support, it was Johnson who committed large numbers of troops and resources to the war effort following the Gulf of Tonkin incident in 1964.