This document outlines several key policies and events that fundamentally changed US foreign policy after WWII in response to the threat of Soviet expansionism. It describes the Truman Doctrine which pledged US support for free peoples against outside threats. It also discusses the Marshall Plan which provided economic aid to prevent Western European countries from turning to communism. Finally, it mentions the creation of NATO as the first US defensive alliance and the National Security Act which reorganized the US military and intelligence communities under the new Department of Defense.