d) Lyndon B. Johnson

In the 1960s, under the administration of U.S. President Lyndon B. Johnson, a crucial shift occurred in the Vietnam War, profoundly impacting global dynamics. The pivotal moment came after the Gulf of Tonkin incident in 1964, which Johnson used as a catalyst to significantly intensify American military engagement in Vietnam. This escalation was largely driven by the United States’ determination to curb the spread of communism throughout Southeast Asia, a key aspect of its Cold War strategy. The consequences of this decision were far-reaching and multifaceted. The prolonged conflict that ensued not only caused extensive devastation in Vietnam but also led to profound social, political, and military repercussions in the United States. It stirred widespread anti-war sentiment, triggered political upheaval, and marked a pivotal moment in American foreign policy, leaving a lasting legacy on both nations’ histories.