The Vietnam War began in 1955, in the midst of the Cold War. During the previous year, Vietnam had been divided into two states: South Vietnam, which was allied with the Western bloc, and North Vietnam, which was allied with communist Russia and China. Supported by North Vietnam, an armed uprising by a new organization called the National Liberation Front for South Vietnam (aka the Viet Cong) sparked the beginning of the conflict, which lasted for two decades.

From the beginning, US President Dwight D. Eisenhower pledged American support for South Vietnam in an effort to curtail the growth of communist influence in Asia, but it wasn’t until 1962, during the John F. Kennedy administration, that US troops became involved. This developed the idea of the domino theory, according to which the fall of one country to communism would lead to others doing the same, like a line of dominoes falling one after the other, provided the rationale for direct US engagement. In 1964, Congress passed the Gulf of Tonkin Resolution, which gave President Lyndon B. Johnson broad power in making decisions about the war, and by 1965, over 100,000 US troops were fighting in Vietnam.