What was the main reason that president truman proclaimed what would become known as the truman doctrine in 1947?

"The Truman Doctrine was an American foreign policy whose stated purpose was to counter Soviet geopolitical expansion during the Cold War."

The main reason that President Truman created the Truman Doctrine was to contain, to hold the spread of communism.

Explanation:

On March 12, 1947, President Truman gave a speech, broadcast over national radio, in which he asked Congress for $400 million in economic aid to Greece and Turkey. Otherwise, the Soviet Union would come to dominate Europe, the Middle East, and Asia. In 1947, Congress passed a Greek-Turkish aid bill that helped Turkey achieve economic stability and enabled Greece to defeat a  communist insurrection in 1949.

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