Truman believed that the events in Greece and Turkey had a long-lasting impact because they represented the first time that the United States had committed itself to actively supporting a nation against communist aggression. In other words, the Truman Doctrine, which was announced in 1947, signaled a major shift in U.S. foreign policy towards a more active and interventionist approach. This policy of containing communism, known as the "domino theory," was based on the idea that if one nation fell to communism, it would lead to a series of other nations falling as well, like a row of dominoes. Truman viewed Greece and Turkey as the first dominoes in this chain, and he believed that if the United States did not take a strong stand against communist aggression in these countries, it would embolden the Soviet Union to expand its influence elsewhere. Therefore, Truman saw the events in Greece and Turkey as significant because they represented a pivotal moment in the Cold War and signaled the beginning of a new era in U.S. foreign policy.
