The cold war began after the end of World War II and is marked as a period of struggle for supremacy between the US and its allies, and the Soviet Union and its satellite states. Although the US and the Soviet Union had fought against Nazi Germany as allies, the alliance began to crumble even before the war was over and stemmed from the disagreement over D-Day that was 6th June 1944, which according to the Soviets was quite delayed as they suffered the most causalities. The post-war discussion for the joint occupation of Germany at the Potsdam Conference was a high-tension affair as the Soviets sought to strengthen their roots in Eastern Europe while the US set out to define a policy containing the spread of communism in Western Europe. In this regard, the Truman Doctrine of 1947 pledged to provide military, economic, and political assistance to the democratic governments threatened by communism. Similarly, The Marshall Plan of 1947 aimed to eliminate political instability that may invite communist occupations. In 1948, the US conducted a massive airlift operation to provide supplies to Berlin for 231 days, after the Soviets cut off all external ties with the city. Furthermore, the role of the US involved joining the “North American Treaty Organization (NATO)” in 1949, which was the first-ever military alliance in US history.