How do these help the U.S. stop spread of communism in the Cold War?

The Domino Theory was used to explain why the U.S. was in Vietnam. It was felt that if one country in Southeast Asia during the 1960s was to fall, the other nations would fall to communism like a line of dominos

The Berlin Airlift was used by the Americans to fly all of the necessities the free West Berlin citizens would need to live as close to normal as possible. The Soviets had closed all highways and railroads surrounding Berlin, which was in East Germany, so the U.S. used the airlift to keep West Berlin functioning - it worked.

The dominoe theory gave the US a reason to keep fighting, airlift gave Germans food and won us German support and helped give the soviet union more enemies