Because of the Domino Theory what kind of foreign policy did the US have?

The domino theory supported an interventionist foreign policy. The US feared to allow any single nation to become communist since that was expect to lead to a whole series of communist take overs. As it turns out, the domino theory was completely wrong. Vietnam did eventually become communist (and remains communist to this day, even after the fall of the Soviet Union) but no other countries became communist as a result, and indeed, global communism is almost extinct.