Vietnam
The United States went to war in Vietnam for multiple reasons but the basic reason was Charles De Gaulle. The American strategy at the time was to contain the Soviet Union with a string of alliances swinging from Norway all the way through [Vietnam], and blocked them through expanding [alliances]. Charles de Gaulle came along and said “you can’t trust the americans because if they ever attacked the Americans wouldn’t come … you you’re going to be left alone we have to form our own NATO independent of the United States”. During the Vietnam War there’s a word that became incredibly important credibility. Credibility meant that how credible were the American guarantees to this all-important structure of containment, how credible was it that we would come to Germany’s aid, or Japan’s aid with everything we had, if they were a war. And a terrible fear that time was that these people would lose confidence in us. So part of the reason we went to Vietnam had nothing to do with Vietnam the fear was that if we didn’t go to Vietnam our credibility with our other allies would be gone and the entire American strategy will collapse on that basis. There was no expectation [we would end up with] 50,000 dead, on that basis the expectation was that we would go into a small police action we may win it, we may lose it, but the Germans would know that our guarantee means something.
LBJ Biography, Into the Quagmire
John F. Kennedy, the new President, affirmed this commitment during a period of rising Cold War tensions which compelled him, however reluctantly, to expand it significantly. Kennedy entered the White House at a crucial juncture in postwar affairs, punctuated by nationalist upheaval and intense Sino-Soviet competition. As the states of Africa and Asia emerged from European rule, China and Russia curried their favor by championing “wars of liberation” from colonial oppression. Interpreting these developments as a challenge to America’s leadership, JFK responded vigorously, pledging the United States to activism in the third world. A series of international crises during his first year intensified Kennedy’s concern for maintaining a non-communist South Vietnam.
In 1961, JFK challenged Castro’s Cuba at the Bay of Pigs with disastrous results; engaged Khrushchev at the stormy Vienna summit; witnessed the construction of the Berlin Wall; and began sensitive negotiations on the neutralization of Laos. Seeing himself on the defensive, Kennedy determined to demonstrate his resolve by standing firm in South Vietnam. …
[After South Vietnamese leader Diem’s repression] Washington began distancing itself from Diem and preparing for a coup. After several false starts, that coup occurred on November 1, 1963. With the Kennedy administration’s tacit consent, a military cabal deposed the regime, abruptly killing both Diem and Nhu.
JFK’s own assassination followed three weeks later. But before his death, America’s commitment to South Vietnam had entered a new and troublesome period. For Diem’s overthrow—however predictable given his peremptory rule—unleashed powerful and unpredictable forces of fateful significance to U.S.-Vietnamese relations. The responsibility for this development rested with John Kennedy; its consequences confronted his successor, Lyndon Johnson. …
During his formative years, Johnson received little exposure to foreign affairs. “When I was a boy,” he later recalled, “we never had these issues of our relations with other nations so much. We didn’t wake up with Vietnam and have Santo Domingo for lunch and the Congo for dinner.”. LBJ focused his attention, quite naturally, on Texas politics, which seemed far removed from international concerns. Johnson utilized his mastery of state affairs to launch a political career, first as assistant to south Texas Congressman Richard Kleberg, then as state National Youth Administration director, and finally as U.S. representative from central Texas. LBJ arrived in Washington as a new congressman just as Hitler’s armies prepared their march across Europe. The western democracies’ belated response to fascist aggression created a lasting impression on the young Johnson. Like many of his generation, LBJ interpreted appeasement as a dangerous seed yielding bitter fruit—a lesson Johnson carried throughout his legislative career and into the White House. “[E]verything I knew about history,” LBJ subsequently remarked, “told me that if I got out of Vietnam … then I’d be doing exactly what Chamberlain did [before] World War II. I’d be giving a big fat reward to aggression”