During the Cold War, the United States was focused on the foreign policy of containment. This idea focuses on stopping the spread of communism on an international scale. This policy explains why the US got involved in Cuba and Vietnam.
In Cuba, Fidel Castro and his followers overthrew Batista and established a communist government. Along with this, Castro established a good trading relationship with the Soviet Union. This resulted in the US attempting to overthrow Castro through the Bay of Pigs Invasion. However, this mission failed and only increased Castro's power and influence in Cuba.
As for Vietnam, the US was always interested in what was happening there, as they were afraid the communist system in North Vietnam would spread to the democratic country of South Vietnam. This act gave President Lyndon B. Johnson the power to take all necessary measures to protect US interests in Vietnam and to increase military action if needed.
