Final answer:
The Truman Doctrine was a policy aimed at supporting countries resisting communism and preventing its spread, serving as an example of containment.
Step-by-step explanation:
The purpose of the Truman Doctrine was to support free peoples who were resisting attempted subjugation by armed minorities or outside pressures, especially against communist forces. It was an example of containment because it aimed to prevent the spread of communism to other countries beyond the ones where it already existed. By providing military aid to Greece and Turkey, the United States successfully helped these countries resist communist pressure and maintain control.