Under the truman doctrine, the united states agreed to

Correct  The US agreed to provide financial and military aid to countries fighting a communist takeover.

Explanation/detail:

The Truman Doctrine was first stated by the president to Congress in 1947, saying:  "It must be the policy of the United States to support free people who are resisting attempted subjugation by armed minorities or by outside pressures."  Essentially, the Truman Doctrine pledged American effort elsewhere in the world to check the spread of communist and Soviet influence.  The policy was first put into action in 1948 by providing economic support to Greece and Turkey to stave off communist movement in those countries.

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