Eastern Europe at that time of Truman's presidency was the only place with communism at that point. Truman's beliefs would be shared with that of the UK, with Churchill declaring that an "Iron curtain" had been built, separating eastern europe from that of the west.
Truman's policy of Containment involved allowing Communism to remain where it was, but preventing it from spreading. As a result, the US would begin helping other countries, by aiding Greece in its civil war and Turkey from being threatened by the USSR. He also concocted the Marshall plan to help countries in western europe from falling to Communism.
