Why was the Truman Doctrine significant?

The Truman Doctrine was an American initiative introduced in 1947, which marked a change of international policy from isolationism to containment. Introduced by President Truman in a speech to Congress, this was launched to obtain financial aid to help Turkish and Greek monarchists fighting against Communists. While the Truman Doctrine does not explicitly mention the Soviet Union, it was clear that it was intended as a warning to Stalin that any further encroachment of the Red Army in Europe would not be accepted. However, when the Truman Doctrine was put into action alongside the Marshall Plan, Stalin felt increasingly betrayed by Western attempts to undermine his control of the Eastern bloc. As a result, ideological rhetoric increased between the two superpowers, as shown by the Soviet leader's condemnation of the joint policy as 'dollar imperialism.' In this light, the Truman Doctrine exacerbated the security concerns of the Soviet Union, and therefore stimulated an atmosphere of mistrust, which ultimately paved the way for the breakdown of the Grand Alliance in succmbing to Cold War hostilities.