Truman Doctrine and Cold War Containment

After World War II, the geopolitical landscape shifted dramatically, leading to the emergence of the Bipolar world order characterized by the rivalry of the United States and the Soviet Union. Different ideological systems, competition for global influence, and conflicts in various regions contributed to the escalating tensions of the Cold War. In the context of these developments, which agreement or initiative marked a significant step by the United States to contain the spread of communism in Europe and aided in shaping the early Cold War strategy?