Final answer:
The Truman Doctrine signalled a shift in U.S. foreign policy to actively prevent the spread of communism, particularly by aiding Greece and Turkey. It was aligned with the policy of containment and later complemented by NATO formation against the Warsaw Pact. Under Eisenhower, a more assertive approach, brinkmanship, was adopted to counter communism.
Step-by-step explanation:
The Truman Doctrine was a significant turning point in U.S. foreign policy, marking a departure from its traditional isolationism and taking a stance to actively prevent the spread of communism after World War II. In March 1947, President Truman called on the United States to support 'free peoples who are resisting attempted subjugation by armed minorities or by outside pressures,' which particularly applied to Greece and Turkey during their respective civil conflicts. With Congress's approval, $400 million in aid was provided to these countries, reinforcing the policy of containment and avoiding the expansion of Stalin's influence beyond the 'iron curtain.' Furthermore, geopolitical strategy during this era led to the creation of the North Atlantic Treaty Organization (NATO) as a collective defense against communist nations, in contrast to the Warsaw Pact, which was the Soviet response, creating a division between Eastern and Western blocs.
Drawing from Kennan's advice on containment, the Truman Administration set out to promote capitalism and democracy as a countermeasure to communism. The introduction of the Marshall Plan, aimed at the economic recovery of Europe, was also part of the wider containment strategy, enabling the stabilisation of democratic governments and the reconstruction of war-torn nations to prevent the rise of communist influences. The subsequent years of the Eisenhower Administration introduced new approaches like 'brinkmanship,' ready to push to the very edge of war to maintain peace and oppose communist aggression.