The Truman Doctrine The Truman Doctrine was the force for change in United States foreign policy, from isolationism to internationalism; which was the main reason for involvement in the two containment wars and world affairs. The Truman Doctrine initiated a major shift in U.S. foreign policy, from aid to Türkiye and Greece to influence over Korea and Vietnam. The aftermath of World War II inspired the United States to issue a doctrine that would stop communist influence throughout the world. However, the United States' passion to implement the Truman Doctrine led to our soldiers dying in Vietnam and Korea for a needless cause. imposed on free peoples... would undermine the foundations of... peace and security of the United States." The Truman Doctrine would change the foreign policy of the United States. This policy would primarily support the democratic governments of Turkey and Greece. These nations were threatened by rebels, supported by the Soviet Union, to overthrow the government and establish a communist regime. Direct influence of this doctrine was the Marshall Plan was designed to provide aid to any European country damaged during the Second World War It contributed greatly to devastating European nations such as Italy and France. By helping them economically, the Marshall Plan indirectly helped to quell the growing communist sentiment in these countries. The process by which the Truman Doctrine came to fruition was long and difficult. After World War II, the Soviet Union and the United States were at the top of world power. By the end of the 1940s, the USSR had caught up with the nuclear weapons programs of the United States. Furthermore, they were very hungry for land. Throughout the history of Russia, they have been looking for a port. In this respect the Soviets posed a direct threat to their non-communist neighbors; Greece, Türkiye and Iran. In Iran, the USSR was not evacuating the northern provinces of Iran despite pleas from the United States. In Türkiye, the Soviet Union desired numerous naval bases along the Dardanelles Strait. Furthermore, they pressured Turkey over the border cessions that Turkey had taken from Russia after World War I.