Divergent objectives: The Allies had entered the war with different goals. The United States and Great Britain sought to defeat Germany and establish a stable postwar order, while the Soviet Union also wanted to expand its influence in Eastern Europe. These divergent objectives made it difficult to reach agreement on key issues.
Competing plans for Germany: The Allies had different ideas about what should be done with Germany after the war. The United States and Great Britain wanted to demilitarize and democratize Germany, while the Soviet Union wanted to divide Germany into zones of occupation and extract reparations. These disagreements made it difficult to reach agreement on a common policy towards Germany.
Personal tensions: The leaders of the Big Three - Harry Truman of the United States, Joseph Stalin of the Soviet Union, and Winston Churchill (and later Clement Attlee) of Great Britain - had very different personalities and styles of leadership. Stalin, in particular, was known for his ruthless and suspicious nature. These personal tensions made it difficult to build trust and rapport between the leaders.
The atomic bomb: The United States' successful test of the atomic bomb in July 1945 changed the dynamics of the conference. Truman informed Stalin about the bomb, but he did not share any details about its power or how it worked. This left Stalin feeling suspicious and uncertain about the United States' intentions.
Emerging Cold War tensions: The Potsdam Conference took place at a time when the wartime alliance between the United States and the Soviet Union was already beginning to fray. This was reflected in the difficulties the Allies had in reaching agreement on key issues, as well as in the increasingly hostile rhetoric between the two sides.
As a result of these factors, the Potsdam Conference was ultimately a failure. The Allies failed to reach agreement on a number of key issues, including the future of Germany, the fate of Poland, and the establishment of a postwar international organization. The conference also marked the beginning of the Cold War, as the United States and the Soviet Union emerged from the war as rival superpowers.