How did the domino theory influence united states foreign policy?

It suggested that the United States would need to support governments fighting communism

Explanation:

The domino theory held that if one region fell to communism, other countries in the region would also fall like a row of dominoes (one right after the other).

Domino theory began to be used as a shorthand expression of the strategic importance of South Vietnam to the United States, as well as the need to contain the spread of communism throughout the world.