The U.S.A. didn’t enter the Vietnam War because of the Cuban Communist revolution near Florida. The Cold War began much earlier, as early as the first Russian revolution when the U.S.A. sent 2000 soldiers to Russia in support the white army fighting the red army. The United States wasn’t willing to give diplomatic recognition to the Soviet Union until 1933. The Nazis were rising then and President Roosevelt may have had a pragmatic interest in establishing relations.
World War II occurred and the U.S. and Soviets became allies to defeat the Nazis. Then with the end of the war and two large winning armies in Europe the continent was largely divided up in two sides; those free nations of the west affiliated with the western allies and those of the east affiliated with Soviet Communism.
Soviet Dictator Joseph Stalin had a row with a rival; Leon Trotsky, and liquidated Trotsky and his relatives in the process of gaining absolute power. He also purged the military of potential security threats to himself before the war. Stalin as absolute dictator believed in communism in one country, Russia, instead of global communism as Trotsky espoused. Of course he kept a tight leash on those eastern European nations rolled up in defeating the Nazis although preponderantly they were not annexed, retaining nominal independence. With Trotsky dead Stalin’s more inward-looking politics of industrializing and rebuilding Russia and increasing it militarily prevailed. Yet with Stalin’s death a Trotsky policy of support for global revolutions commenced. Communist revolutions around the world were supported by the Soviet Union intensifying the Cold War.
Stalin died in early 1953. The Korean War was already in progress. That war occurred from 1950 until 27 July 1953 because of the ideological cold war between communism and free enterprise democracy. The two incompatible systems required two separate nations in Korea, so the United Nations ordered elections for a government for the South and the Northern Communists invaded starting the conflict.
China supported the North Koreans. The United States was the major ally of the South Koreans although numerous United Nations forces participated. The U.S.A. already had military advisers in Vietnam. The U.N. also recognized two nations divided along the same lines as Korea, and thus a war was fought in Vietnam too.
The N. Vietnamese regarded the war as anti-colonial conflict battling the French and as a civil war fighting against the South. The United States supported the South in Vietnam as it had in Korea with different results.
The Cuban revolution was not an anti-colonial revolution. It was the United States that liberated Cuba from Spain acting in a sense with paradigmatic symmetry with that of Russia supporting the liberation of Vietnam from colonization as part of French Indochina. Vietnam was colonized by the French from 1887 until 1954.
Because the Soviet Union with its vast and growing nuclear weapons arsenal was an empirical threat to the free world, the Eisenhower administration was conservative in trying to control or contain communist revolutions globally. Even formerly friendly nations such as Iran became distrusted. The U.S.A. sponsored a coup to end the democratically elected government under Prime Minister Mossadegh who had nationalized Iranian oil fields. He did that because Anglo-Iranian oil owned the oil rights and wouldn’t let Mossaddegh look at the books. Winston Church and Eisenhower organized a coup and let the Shah have the country. He ruled like a dictator friendly to the west. That happened in August 1953- it was a busy year.
The Cuban revolution occurred between 1953 and 1959. It was another communist insurgency to overthrow an oppressive government. It was difficult in the 50s and 60s to have a non-communist revolution overthrow an oppressive government although many were worthy of one. Unfortunately colonialism of Brits and other European nations along with dictators in former colonies were conflated with communist propaganda and support in revolutionary movements. Vietnam also fell in to the juxtaposition of wars of liberation, war against dictators, was against communist globalism etc that were all concurrent thematic elements of the ropes humanity hung itself with in that time. Each had valid reasons for existing, tragically, with the probably exception of the dictators who generally had anti-communism as their valid premise for existing, and that in some respects was just a borrowed excuse valid more externally rather than domestically.
Wars for survival of the west and freedom generally against global communism sponsored by the Soviet Union and Communist China clashed with numerous local liberation movements that were supported by real globalists for communism, even if the local revolutionaries were motivated more for local empowerment. It was all an ideological mess especially with capitalism thrown into the mix that eventually would evolve in global corporatism and plutocracy cozying up with Chinese Communist elites.