Final answer:
The Truman Doctrine represented a shift from US isolationism to an interventionist foreign policy with a focus on containing Communism. It committed the US to support nations threatened by Communist insurgencies and set the stage for American involvement in foreign conflicts throughout the Cold War.
Step-by-step explanation:
How the Truman Doctrine Changed US Foreign Policy :
The Truman Doctrine marked a significant shift in US foreign policy in the aftermath of World War II. Prior to its announcement, the United States had largely embraced a policy of non-intervention and isolationism. However, influenced by the threat of Communist expansion in nations like Greece and Turkey, President Truman declared in March 1947 that it must be the policy of the United States to support free peoples who are resisting subjugation by armed minorities or outside pressures. This directly translated into a proactive commitment to contain the spread of Communism globally.
On March 12, 1947, Truman directly appealed to Congress and successfully convinced the nation to provide military aid to the monarchies of Greece and Turkey, symbolizing a break from the nation's previous stance of isolationism. The Truman Doctrine effectively ushered in an era of containment of Communism, asserting the US role in international affairs as a defender of democracy and marking a longstanding strategy of countering Soviet influence during the Cold War.