The Potsdam Conference was held at Cecilienhof, the home of Crown Prince Wilhelm Hohenzollern, in Potsdam, occupied Germany, from 17 July to 2 August 1945. (In some older documents it is also referred to as the Berlin Conference of the Three Heads of Government of the USSR, USA and UK.

Participants were the Soviet Union, the United Kingdom and the United States. The three powers were represented by Communist Party General Secretary Joseph Stalin, Prime Ministers Winston Churchill and, later, Clement Attlee, and President Harry S. Truman.

Stalin, Churchill, and Truman—as well as Attlee, who participated alongside Churchill while awaiting the outcome of the 1945 general election, and then replaced Churchill as Prime Minister after the Labour Party's defeat of the Conservatives—gathered to decide how to administer the defeated Nazi Germany, which had agreed to unconditional surrender nine weeks earlier, on 8 May (V-E Day). The goals of the conference also included the establishment of post-war order, peace treaty issues, and countering the effects of the war.

Truman had mentioned an unspecified "powerful new weapon" to Stalin during the conference. Towards the end of the conference, Japan was given an ultimatum to surrender (in the name of the United States, Great Britain and China) or meet "prompt and utter destruction", which did not mention the new bomb. Prime minister Kantarō Suzuki did not respond (mokusatsu, which was interpreted as a declaration that the Empire of Japan should ignore the ultimatum).

Therefore, the United States dropped atomic bombs on Hiroshima on August 6 and Nagasaki on August 9, 1945. The justification was that both cities were legitimate military targets, to end the war swiftly, and preserve American lives. However, to some the timing has suggested that Truman did not want Stalin involved in the terms of Japan's surrender. It is important to note that Truman delayed the Potsdam Conference in order to be sure of the functionality of this "powerful new weapon."

Notably, when Truman informed Stalin of the atomic bomb, he did not explicitly mention its atomic nature, just vaguely saying that the United States “had a new weapon of unusual destructive force”; Stalin, though, had full knowledge of the atomic bomb's development due to Soviet spy networks inside the Manhattan Project, and told Truman at the conference to "make good use of this new addition to the Allied arsenal".

The Soviet Union converted the other countries of eastern Europe into Soviet Satellite states within the Eastern Bloc, such as the People's Republic of Poland, the People's Republic of Bulgaria, the People's Republic of Hungary, the Czechoslovak Republic, the People's Republic of Romania, and the People's Republic of Albania.

The Soviets later formed the puppet state of East Germany (officially The German Democratic Republic) from the Soviet zone of German occupation