Final answer:
President Truman requested Congress to provide $400 million in aid to help Greece and Turkey fight the spread of communism, as part of the Truman Doctrine, which became a key element of U.S. Cold War policy.
Step-by-step explanation:
In response to the rise of Communist parties in Greece and Turkey and the possibility of a Communist takeover in these countries, President Truman addressed Congress on March 12, 1947, to propose assistance to prevent the spread of communism. This proposal was known as the Truman Doctrine, a hallmark of U.S. Cold War policy. Truman asked Congress to grant aid amounting to $400 million to help Greece and Turkey combat the influence and expansion of communism. Moreover, Britain's withdrawal from the region due to economic constraints prompted the U.S. to extend support through financial assistance, weaponry, and military training.
Fortified by the Truman Doctrine, the Greek government eventually succeeded in defeating communist rebels, while Turkey was able to resist Soviet pressure and maintain control of the strategically important Dardanelles. The Truman Doctrine represented a profound shift in American foreign policy, committing to the containment policy developed by George Kennan, and signifying a departure from traditional non-interventionist stance, which had shaped U.S. policy prior to World War II.