Final answer:
President Truman used the policy of containment to prevent communism from spreading beyond its existing boundaries, focusing on economic policies and forming alliances to keep Soviet influence within Eastern Europe.
Step-by-step explanation:
President Truman attempted to prevent the spread of communism beyond its existing boundaries using a policy known as containment. This policy aimed to restrict Soviet influence to Eastern Europe, countering the global threat perceived by US policymakers due to Communism and the Soviet Union. Truman's strategy suggested that rather than changing the communist situation within the Soviet Union and its controlled Eastern European countries, efforts should focus on preventing its expansion to other parts of the world.
Containment was a central tenet of Cold War policy for the United States and was based on proposals by George Kennan, who sent the "Long Telegram" recommending this strategy. The policy suggested that communism, if contained, would eventually fail without spreading to other countries. This approach emphasized the need for the United States to exert economic and diplomatic efforts, as well as form alliances, to secure areas around the Soviet Union and prevent the further spread of communism.