<P> The alliance between the Western Allies and the Soviet Union began to deteriorate even before the war was over, when Stalin, Roosevelt, and Churchill exchanged a heated correspondence over whether the Polish government - in - exile, backed by Roosevelt and Churchill, or the Provisional Government, backed by Stalin, should be recognised . Stalin won . </P> <P> A number of allied leaders felt that war between the United States and the Soviet Union was likely . On 19 May 1945, American Under - Secretary of State Joseph Grew went so far as to say that it was inevitable . </P> <P> On 5 March 1946, in his "Sinews of Peace" (Iron Curtain) speech at Westminster College in Fulton, Missouri, Winston Churchill said "a shadow" had fallen over Europe . He described Stalin as having dropped an "Iron Curtain" between East and West . Stalin responded by charging that co-existence between communist countries and the West was impossible . In mid-1948 the Soviet Union imposed a blockade on the Western zone of occupation in Berlin . </P> <P> Due to the rising tension in Europe and concerns over further Soviet expansion, American planners came up with a contingency plan code - named Operation Dropshot in 1949 . It considered possible nuclear and conventional war with the Soviet Union and its allies in order to counter a Soviet takeover of Western Europe, the Near East and parts of Eastern Asia that they anticipated would begin around 1957 . In response, the US would saturate the Soviet Union with atomic and high - explosive bombs, and then invade and occupy the country . In later years, to reduce military expenditures while countering Soviet conventional strength, President Dwight Eisenhower would adopt a strategy of massive retaliation, relying on the threat of a US nuclear strike to prevent non-nuclear incursions by the Soviet Union in Europe and elsewhere . The approach entailed a major buildup of US nuclear forces and a corresponding reduction in America's non-nuclear ground and naval strength . The Soviet Union viewed these developments as "atomic blackmail". </P>

What occurred immediately after world war ii ended in the united states