The Korean War turned the Cold War into a global issue rather than a European one and worsened tensions between the East and West. Russia flooded aid into China and consequently, the two Communist giants became less trusted and more feared.
America was very committed to a theory called the "Domino Theory" and the Truman doctrine of containment. America believed that Communism was likely to spread very rapidly if left, and if just one country fell to it then many others would follow, just like a game of dominos. This feeling was present during all of the U.S. presidencies.
When Lyndon Johnson became President, he was a very firm believer of the Domino theory and had a complete hatred of Communism. In 1964 there was a choice to be made, the Communists were about to win this war so either America would withdraw from Vietnam, going against their anti-communist ideas, or escalate it.
Johnson took the latter, and under the cover of the Gulf of Tulkin Incident, within one year, the amount of troops was escalated to 60,000 from the original 16,000. The Gulf of Tulkin involved two American destroyers, and a supposed unprovoked attack. The truth was that the destroyers were aiding a South Vietnamese attack on North Vietnam. Nevertheless, Johnson used this to persuade Congress to go to war. Without a proper discussion they "Americanized" North Vietnam, the advisors became combat troops, and officially America went to war.
Many Americans supported the United States involvement in the War in agreement with the government that American assistance was needed in order to stop the spread of Communism. Other people felt that it was immoral for the United States to involve itself in another country's internal matters.
The antiwar movement against Vietnam in the US from 1965-1971 was...