The beginning of Vietnam conflict can be traced to the Second World War, when the Americans helped Ho Chi Minh in his fight against Japan. After the war ended, the Cold War began between the United States and the Soviet Union, which, at the time being, were the largest global powers. Both powers wanted to gain control of the new territories in order to promote their ideology and expand their influence. When this competition for areas reached Vietnam, the United States could not resist another chance to oppose spread of communism, especially taking into consideration the fact that China’s civil war resulted in communists’ win. The United States could not engage into direct confrontation with Russia, because the latest already had nuclear weapons, therefore, both countries fought against each other on ‘neutral’ territories. All in all, the United States entered the Vietnam War to support and promote American ideology, to confirm American ego, and in line with Eisenhower’s Domino theory.
The desire to promote American capitalist ideology rather than communist ideology promoted by North Vietnam was one of the major reasons for entering war. The Harry Truman administration, as early as May of 1945, assured Paris that, without reservation, the United States fully recognized her sovereignty over Vietnam, Cambodia, and Laos. That was of relatively marginal importance in determining the course of postwar events there. This early U.S. role from 1945 to 1949 was critical in setting the stage for and influencing the direction of the subsequent and much better known U.S. policies in the 1950s and 1960s. The Truman administration's injection of power into Vietnam had a very heavy impact on the course of both military and political developments there. Without it, Ho Chi Minh's Vietminh would probably have come to control all of Vietnam within a year or two of the departure of Allied occupation forces in mid-1946.
Domino theory, which was promoted by President Eisenhower, basically states that the more countries fall under rule of communism, the more the chances are that neighboring countries will be affected as well, and this will hurt capitalist countries, including America. In seeking the origins of the U.S. involvement in Vietnam, there is often a tendency to project backward into time only part way - to periods which are today most clearly understood and most deeply etched in the public's memory but which do not explain how the process actually began. Thus, the domino theory has significant bearing on explain how and why the United States originally became enmeshed in Vietnam. These perceptions emerged only after - well after - the United States had taken a clear stand in Vietnam in support of France and its effort to counter the main thrust of Vietnamese nationalism. They help explain how the United States stayed on once it had taken that stand, but not how it had gotten into that exposed position in the first place. Although the perception is widespread, it is artificial and misleading to divide the thirty years of post-World War II foreign intervention in Vietnam into an initial nine-year French war and a subsequent twenty-one year U.S. period. In fact, the United States was deeply and critically involved from the very beginning, commencing in October 1945, and from the outset the war was to a major extent American as well as French--even though the U.S. public did not realize this.
American ego also was an important factor that affected the country’s entering Vietnam War, as America wanted to help France, thus showing its superiority. For many researchers It is very difficult to understand how the United States was drawn into Vietnam without an appreciation of the French perception of Vietnam's place within the whole of France's vast overseas empire. Just as Washington's policies toward Vietnam were rooted primarily outside of that country, so too was this the case with Paris. For French policymakers, Vietnam itself was of relatively minor economic or strategic importance, and if that country alone had been involved they would probably never have made the enormous effort they did to reconquer the country. However, they saw Vietnam in terms of the whole of their huge overseas colonial empire, and it was because of this that for them, by the fall of 1945, Vietnam had lost its marginality and became transformed into the very keystone of that empire. It was in Vietnam that the first major postwar nationalist challenge to French colonial authority was mounted, and Paris saw this as a threat to the integrity of its empire as a whole. French officials regarded colonial nationalism as contagious, and their sensitivity to this prospect was exemplified in their ten-pin theory of empire. This had a dynamic rather akin to the subsequent U.S.-coined domino theory, but was much better grounded in reality.
It is apparent that primary reasons for America to enter Vietnam war were to support and promote American ideology, to confirm American ego, and in line with Eisenhower’s Domino theory.The United States did not then wait until early 1950 - as some accounts would have it - to engage its power in Vietnam. Its public support of France's unhappy protégé, the resurrected Emperor Bao Dai, was at that time no real bench mark. Neither was its launching in that year of an openly acknowledged program of economic assistance to the French military campaign in Vietnam. These events were of minor importance in comparison to the very high level of largely covert U.S. involvement during the previous four and a half years-that is, beginning in the fall of 1945. The United States wanted to assure that communism would not spread in Vietnam, facilitating spread of this hostile for capitalism ideology in the neighboring countries.