Why did the US enter the Vietnam War?
If you are operating from a textbook or some type of instructor analysis, I would suggest consulting these sources first and building from there. Different individuals will have different analyses to explore this topic. I would say that the fear of Communism helped the United States to enter the war and commit itself to an escalation of troops within the region. Once the Vietnamese had removed the French colonial influence in the region, a Communist North and supposedly democratic South partition of the region developed. American political and military advisers were concerned about the presence of a Communist North coexisting with its Southern neighbor. The belief at the time was in something called the "domino theory," which articulated that if one nation in a particular section of the world "went Communist," it would only be a matter of time before all of the nations would follow accordingly. This fear helped to increase the United States presence in South Vietnam. At the time, few in America understood that North Vietnam did not seek to dominate the South, but rather believed in its own autonomy, its own freedom from external control. Yet, American interests and political sensitivity believed in the domino theory and committed itself to stopping the spread of Communism in the region with its first advising and then escalation of military forces in the South of Vietnam.