The main argument used to support U.S. military involvement in Vietnam was the fear of the Domino Theory. The Domino Theory was a belief that if one country in a region fell to communism, then neighboring countries would also follow suit, like a row of falling dominos. In the context of Vietnam, it was feared that if Vietnam fell to communism, other nations in Southeast Asia could also become communist, leading to the spread of communism throughout the region.
This concept was a significant factor in the U.S. decision to intervene in Vietnam to prevent the perceived domino effect of communism spreading across Southeast Asia. The Domino Theory provided a rationale for the U.S. to commit military resources to support South Vietnam and prevent the fall of the country to communism.
In summary, the main argument supporting U.S. military involvement in Vietnam was the fear of the Domino Theory, which highlighted the concern that the spread of communism in one country could lead to the spread of communism to neighboring countries in the region.
