Final answer:
The Truman Doctrine was a U.S. policy established in 1947 that promised support to nations at risk of falling under communist control, beginning with substantial aid to Greece and Turkey to prevent the spread of communism. This doctrine reflected America's commitment to the containment of communism and shaped U.S. foreign policy throughout the Cold War.
Step-by-step explanation:
The Truman Doctrine was a significant policy statement by President Harry S. Truman in 1947, setting a precedent for the United States to provide support to countries threatened by communism. The doctrine stemmed from the geopolitical situation in Greece and Turkey, where communist forces were gaining momentum. After Britain withdrew its support, the United States stepped in to aid these nations to prevent the spread of communism, committing $400 million to support their governments.
On March 12, 1947, President Truman addressed Congress and made a case for U.S. intervention as a moral duty to support "free peoples" against totalitarian regimes. This led to America playing an extensive role in the containment policy during the Cold War, marking a departure from its previous policy of non-intervention.
As part of the Truman Doctrine, the U.S. not only helped Greece and Turkey but also extended support to other countries at the risk of falling under communist influence. This policy position effectively articulated the American stance of counteracting communism globally, which was a central component of the U.S. foreign policy in the following decades.