The Bombs: Since the invention and detonation for the first ever atomic bomb, the USA felt confident that they were the "best superpower" for the whole world, and ultimately may Western European nations side and ally with the USA for safety. Truman (then the president of the USA) felt ore confident about America if there were to be a conflict between them and the Soviet Union, because America would be "stronger". However, Stalin (Leader of the USSR) felt more determined to occupy Eastern Europe as a "buffer zone" in case the Cold War would escalate into World War. But with the existence of the atomic bombs themselves, both sides of the Cold War were incredibly scared of their own nukclear weapons, because the weapons were a cause of mutually assured destruction, meaning that millions of people could be killed instantly (a possible cause of human extinction. Truman did not trust Stalin, so he didn't tell Stalin about the detonation of the two bombs in Hiroshima and Nagasaki (Japan).