America's Foreign Policy Practice Exam 2026 - Free Practice Questions and Study Guide

President Johnson's rationale for U.S. involvement in Vietnam primarily stemmed from the desire to support and protect South Vietnam from the perceived threat of communist expansion. This consideration was rooted in the broader context of the Cold War, where the United States aimed to contain communism globally.

Johnson believed that failing to support South Vietnam would lead to a domino effect, where neighboring countries would also fall under communist influence, thereby undermining American interests and security. His administration articulated a commitment to defend South Vietnam, which he saw as a promise to uphold the integrity and sovereignty of an ally that was threatened by North Vietnamese aggression.

Johnson often emphasized the importance of maintaining U.S. credibility and honor in international affairs, suggesting that backing down would send a negative message to other nations regarding American reliability. This commitment influenced his decision to escalate U.S. military involvement, as he sought to convey solidarity with South Vietnam and demonstrate the United States' resolve to combat the spread of communism in the region.

Therefore, the rationale relates directly to the idea of fulfilling a promise, as it exemplifies the U.S. commitment to its allies while addressing the larger strategic goals of containing communism.