In attempts to contain communism, Congress by Truman's reccomendation passed an aid package of millions of dollars to send to Greece and Turkey to fight of the communist rebels and protect against the Soviet Union advancement.
The Truman Doctorine
For Greece and Turkey!
The North Atlantic Treaty Organization was created in 1949 by the United States, Canada, and several Western European nations to provide an alliance between the countries joined and protect each other against the Soviet Union
This happened when the Soviet Union cut off all road, rail, and water access to West Berlin. The United States in response, starting airlifting supplies to Berlin which they continued to do for over a year.