Final answer:
During the Cold War, the United States opposed Communism in Vietnam by supporting South Vietnam against the Communists in the north. President Lyndon Johnson had to decide whether to pull out of Vietnam or fully engage in the conflict.
Step-by-step explanation:
During the Cold War, the United States opposed Communism wherever it emerged. Vietnam was one such case. Supporting South Vietnam against the Communists in the north started not long after the defeat of France. By 1960, US advisers were working to bolster South Vietnam's military power. After the assassination of John F. Kennedy, President Lyndon Johnson had to make a choice to either pull out of Vietnam or push the US military to fully engage the Communists in North Vietnam.