Identifying the Initial U.S. Response to Cold War Tensions

In the aftermath of World War II, the geopolitical landscape underwent significant changes as tensions rose between the United States and the Soviet Union. This period marked the beginning of the Cold War, a conflict characterized by ideological, political, and military rivalries. One of the foundational events leading to the Cold War was the implementation of various policies and doctrines aimed at containing communism. Which of the following events or strategies is primarily associated with the initial U.S. response to the threat of Soviet expansion post-World War II?