The US was determined to implement a foreign policy of containment towards the USSR since the beginning of 1945. The US disagreed to requests Stalin made at the Yalta and Potsdam conference, which served to limit Stalin's power and control over Europe. President Truman became even more concerned after receiving George Kennan's Long Telegram in February 1946. This telegram was sent by the US ambassador in Moscow, reporting on the destructive intentions of the USSR. Truman made his policy clear the next year as he declared that it was America's duty to intervene and help countries in protecting themselves against communist attacks. However, the policy of containment did not prove to be as effective as it was hoped. More failures than successes resulted during the cold war.
The first steps the US took in containing communism were unofficial: There were several disagreements reached during the Yalta conference (Feb 1945) and the Potsdam conference (July 17th 1945).
These disagreements were ones that concerned Stalin's requests such as Soviet policy in Poland, size of reparations from Germany, and naval bases in the Straits (Dardanelles). These requests were all to increase Soviet influence over Europe, and by disagreeing to these, the US clearly made her point to contain communism. The containment of communism by agreements proved to have been the most effective compared to other methods and policies.
After receiving the Long Telegram, Truman became even the more concerned about containing communism. However, it was not until March of the next year that he made his policy clear. On March 12 Truman made a speech as a response to the UK's request of aid in dealing with the Greek civil war, where communists were taking over the country. In Truman's speech he announced that they would provide military aid to countries under...