Truman pursued an aggressive foreign policy in response to the rise of communism in the postwar world. Some key aspects included establishing the UN for international cooperation, occupying Japan to rebuild it as a democracy, and implementing the containment policy to rollback Soviet expansion in Europe and Asia through policies like the Truman Doctrine and Marshall Plan. This involved providing economic and military aid to countries threatened by communism like Greece, Turkey, and West Berlin during the Berlin Airlift crisis. However, communism still spread to China which became a loss for Truman's containment efforts.