b) Lyndon B. Johnson

President Lyndon B. Johnson’s decision to send American troops to Vietnam in the 1960s was a defining moment in U.S. foreign policy, setting the stage for deeper American involvement in the Vietnam War.  Johnson’s administration provided military advisors and support to South Vietnam as part of its strategy to contain communism in Southeast Asia. This initial deployment marked the beginning of a significant and controversial U.S. military presence in Vietnam, which escalated under subsequent administrations. Johnson’s actions reflected the Cold War era’s domino theory, wherein the fall of one country to communism was believed to lead to the spread of communism in neighboring countries.