Why did the united states support france in vietnam?

Initially, U.S. supported decolonization or the removal of Vietnam as a colony. However, they wanted France as an ally in its Cold War effort to contain the Soviet Union (now Russia). President Truman wanted to make sure that there was a strong, anticommunist Western Europe. Thus, he sacrificed his own belief of decolonization. To guarantee French aid in the Cold War, Truman supported France's efforts to regain control over Vietnam. Between 1950 and 1954, the U.S. contributed 2.6 billion dollars to France's war efforts.

When President Eisenhower took office, he continued Truman's policies toward Vietnam. He believed in the domino theory, that if Vietnam became a communist country, all other countries in Southeast Asia would follow.