The Potsdam Conference is perhaps best known for President Truman`s conversation with Stalin on July 24, 1945, during which the president informed the Soviet leader that the United States had succeeded in detonating the first atomic bomb on July 16, 1945. Historians have often interpreted Truman`s somewhat firm stance during the negotiations with the U.S. negotiating team`s belief that U.S. nuclear capabilities would strengthen its bargaining power. Stalin, however, was already well informed about the US nuclear program, thanks to the Soviet intelligence network; He has therefore also stood firm in his positions. This situation made the negotiations difficult. The leaders of the United States, Britain and the Soviet Union, who had remained allies throughout the war despite their differences, never met again to discuss cooperation in post-war reconstruction. Debates over whether the new governments should be recognized in some of the defeated Axis powers were even more bitter. The Americans and the British wanted Italy to be immediately admitted to the United Nations. But they refused to recognize Eastern European countries like Romania and Bulgaria until their governments imposed by the Soviet Union were replaced. Churchill gave a long and effusive speech about the fact that Italy was a democracy while the others were not. “Fiction,” Stalin exclaimed.
The exchange went up in flames and no progress was made. Allied leaders had previously decided that a defeated Germany should be divided into four occupation zones. Each area was to be administered by one of the main Allied forces, namely the United States, the Soviet Union, Great Britain and France. Berlin was also divided, as was Austria and its capital, Vienna. Although the areas should be monitored separately, they should be united in common policies by the Control Council in Berlin. Very little was agreed in Potsdam. The three leaders had many differences of opinion at the time: since Italy`s disposition was one of the most important issues that required the attention of the new Council of Foreign Ministers; The three governments were particularly concerned about the conclusion of a peace treaty with her, especially since Italy was the first of the Axis powers to break with Germany and participate in Allied operations against Japan. In the five months since the Yalta Conference, a number of changes have taken place that have significantly affected relations between leaders. The Soviet Union occupied Central and Eastern Europe, and the Red Army effectively controlled the Baltic States, Poland, Czechoslovakia, Hungary, Bulgaria and Romania. Refugees have fled these countries.
Stalin had installed a communist puppet government in Poland, insisted that his control of Eastern Europe was a defensive measure against possible future attacks, and claimed that this was a legitimate sphere of Soviet influence.  The Soviet Union submitted to the Conference a proposal on the territories under mandate, in accordance with what was decided at the Yalta Conference and the Charter of the United Nations. Poland`s border became the Oder and Neisse to the west, and the country received part of the former East Prussia. This necessitated the relocation of millions of Germans to these regions in Germany. The governments of Romania, Hungary, and Bulgaria were already controlled by the Communists, and Stalin stubbornly refused to let the Allies intervene in Eastern Europe. In Potsdam, Truman told Stalin about the “new weapon” of the United States (the atomic bomb) that it wanted to use against Japan. On July 26, the conference issued an ultimatum to Japan calling for unconditional surrender and threatening harsher airstrikes. After Japan rejected this ultimatum, the United States dropped atomic bombs on Hiroshima and Nagasaki.
At the Potsdam meeting, the most urgent issue was the fate of Germany after the war. The Soviets wanted a united Germany, but they also insisted that Germany be completely disarmed. Truman, along with a growing number of U.S. officials, had a deep suspicion of Soviet intentions in Europe. The massive Soviet army already occupied much of Eastern Europe. A strong Germany may be the only obstacle to Soviet domination over all of Europe. In the end, the Big Three agreed to divide Germany into three occupation zones (one for each nation) and to postpone discussions on German reunification to a later date. The other notable topic in Potsdam was one that was practically unsaid. Just as he came to the conference, Truman was informed that the United States had successfully tested the first atomic bomb. Hoping to use the weapon as a means of exerting pressure on the Soviets in the postwar world, Truman casually mentioned to Stalin that America was now in possession of a weapon of monstrously destructive power.
The president was disappointed when the Soviet leader simply replied that he hoped the United States would use this to quickly end the war with Japan. The Declaration of the Potsdam Conference on Germany states: “The Allies intend to give the German people the opportunity to prepare for the eventual restoration of their lives on a democratic and peaceful basis.” The four zones of occupation of Germany, designed at the Yalta Conference, were established, each to be administered by the commander-in-chief of the Soviet, British, American or French occupation armies. .