Which event in Europe after World War 2 was responsible for the beginning of the Cold War?

Let's say this first. America needed desperately to end the war. We were tired, and now more in debt then ever. We made the atomic bomb to drop on Japan. War in Europe ended. We would have gone on shore into main land Japan, BUT Russia declared war, and were already starting their move on Japan. We made the A-bomb and dropped it on Hiroshima and Nagasaki. War Over. Russia saw our bomb, and wanted one similar. Russia is communist, and like Hitler, wanted World Domination, with nukes though. Albert Einstein and Warner Von Braun were immigrants to America that built rockets and the bomb. They're from Germany. Russia had captured Germans, so they did the same. We were at high tensions between them, until the government eventually fell apart in 1992.