How did the Truman Doctrine shape US foreign policy after World War II?
Harry Truman's successful policy of military aid to Greece and Turkey following World War II was key in his decision to make that the cornerstone of US Cold War foreign policy. From then on, until the end of the Cold War in 1991, we can see a consistent theme with each President of giving military foreign aid to, and forming defensive alliances with, countries facing communist threats.
This doctrine gets us involved in the Chinese Civil War, the Berlin Airlift, NATO, and the Korean War, just on Truman's watch. But we can see other presidents building on Truman's example with our efforts to contain Cuba, provide military aid in Latin America and Africa, as well as funding insurgencies against Soviet influence, not to mention our long involvement in the Vietnam War.