What is the historical significance of the Truman Doctrine?

Question: What is the historical significance of the Truman Doctrine!?
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It was created to fight the spread of Communism, as the government was afraid that if a few small, weak countries became Communist, then it would lead to a Domino effect that would lead other countries to fall to Communism, and would hurt the US's idea of free trade and capitalism!.Www@QuestionHome@Com

it was made to help any nation that did not want to be under communist rule with military and economic aid!. Greece and Turkey called on the US to help them fight Communist rebels!. It is significant because it committed the US to the role of fighting and resiting communism worldwide!.Www@QuestionHome@Com