A number of presidents in American history have created a doctrine of how the nation will go about foreign policy in the foreseeable future. For example there was the Monroe Doctrine, the Bush Doctrine, and the one I want to talk about here, the Truman Doctrine.
The Truman Doctrine was the foreign policy that President Harry Truman practiced while he was in office and was the foreign policy that was practiced for the next 20 years, at least. The Truman Doctrine stated
“It must be the policy of the US to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressures.”
The Truman Doctrine basically was the beginning of America acting like a police force around the world and the end of America being more isolationist on the world stage. It also initiated a policy of Containment that would be used under Truman and later abandoned by President Eisenhower when he and his Secretary of State adopt the policy of Brinkmanship.
Another big aspect of the Truman Doctrine was the spreading and supporting of democracy around the world. An instance of this is when in 1947, President Truman requested $400 million to support democracy in Greece and in Turkey from Congress. Also he would soon after recognize Israel as a bastion of democracy in the Middle East.