How did the domino theory affect the ways in which the united states approached both domestic affairs and international relations?

The domino theory postulated that if someone falls to communism, or a country becomes communist, that all around it will also follow. That's why on domestic policies they went on a witch hunt against communists so as to prevent them from spreading their influence, while in foreign affairs they invaded countries like Korea, Vietnam, Afghanistan, an all others where communism was being spread.