[161] With the Soviet Union expanding its sphere of influence through Eastern Europe, Truman and his foreign policy advisors took a hard line against the USSR. In this, he matched U.S. public opinion which quickly came to believe the Soviets were intent upon world domination.[162]
Although he had little personal expertise on foreign matters, Truman listened closely to his top advisors, especially George Marshall and Dean Acheson. The Republicans controlled Congress in 1947–1948, so he worked with their leaders, especially Senator Arthur H. Vandenburg, chairman of the powerful Foreign Relations Committee.[163] He won bipartisan support for both the Truman Doctrine, which formalized a policy of Soviet containment, and the Marshall Plan, which aimed to help rebuild postwar Europe.[164][165]
To get Congress to spend the vast sums necessary to restart the moribund European economy, Truman used an ideological argument, arguing that communism flourishes in economically deprived areas.[166] As part of the U.S. Cold War strategy, Truman signed the National Security Act of 1947 and reorganized military forces by merging the Department of War and the Department of the Navy into the National Military Establishment (later the Department of Defense) and creating the U.S. Air Force. 