Final answer:
President Lyndon Johnson's administration marked a significant intensification of U.S. military involvement in the Vietnam War compared to previous administrations, with over half a million troops deployed and a firm commitment to the war despite growing public opposition. The Gulf of Tonkin Resolution marked the official escalation, while the domino theory influenced the policy decisions. Contrastingly, the incoming Nixon administration outwardly appeared to shift towards ending the war but privately sought to continue the fight.
Step-by-step explanation:
During the Cold War, the U.S. adopted a foreign policy dedicated to containing Communism, and the involvement in Vietnam showcased this global commitment. Previous administrations before President Lyndon Johnson, including that of President Kennedy, had already started supporting South Vietnam through military advisors and other assistance. However, it was under Johnson's administration that the U.S. escalated its involvement significantly. The Gulf of Tonkin Resolution in 1965 was a pivotal moment that saw the Johnson administration greatly increase the deployment of U.S. troops to Vietnam, rising to over half a million soldiers.
The President Johnson's decision to increase military engagement was also influenced by the domino theory, which posited that the fall of one country to Communism in Southeast Asia could lead to the widespread adoption of Communism in neighboring countries. Despite growing public opposition and protests, particularly among college students, Johnson remained committed to a policy of gradual escalation. Public opinion was divided into 'doves' and 'hawks', with approximately two-thirds of Americans initially supporting the war effort during Johnson's administration.
By the end of 1968, public sentiment had shifted enough to affect political strategy, and President Nixon, entering office, presented a front supportive of ending the war. Nevertheless, a gap existed between his public stance and private intentions, as evidenced by his actions that sabotaged Johnson's peace talks with the North Vietnamese.