The most important reason as to why the United States became involved in Vietnam was the long term cause of the Domino Theory. The Domino Theory was the belief that once one country had fallen to communism, its neighbours would do the same. It was devised by John Foster Dulles, the US Secretary of State, during the 1950s. The Domino Theory would be a an obstacle for the Americans if they were to win the Cold War, as they had to keep as few countries from going communist as possible. If South Vietnam were to fall communist, its neighbours in South East Asia may do the same- including India, a country with a billion inhabitants and around 90% of its people living in poverty. Communism may look an attractive prospect to South East Asia’s poor, which increases the likelihood of the Domino Theory, and would have a dire effect for American economic interests in the region. American companies would be nationalised by the state under communism, and trade would be badly affected because Americans would not be able to sell commodities in communist countries. This would not only harm America’s economy, but also its military- it would not be able to sustain a well trained, well equipped army without the money to do so. Eventually, this would also have dire political effects for America- its President would look weak, and the Soviet Union would be the dominant global power, due to the United States’ inferior military, economy and financial system. Moreover, if the…