The Potsdam Conference with the U.S., British, and Soviet heads of state. The day of the conference was set by U.S. President Harry Truman to coincide with completion of the atomic bomb.
July 25, 1945
Courtesy of Harry S. Truman Library
In May 1943, the U.S. was planning to use the bomb not on Germany but Japan. The following September, the U.S. and British leaders agreed to use the bomb against Japan. After spring 1945, with Japan in an extremely weak position, the United States was considering the following ways of bringing the long war to an end: invade the Japanese mainland in November 1945, ask the Soviet Union to join the war against Japan, assure continuation of the emperor system, or use the atomic bomb. The U.S. believed that if the atomic bomb could end the war, Soviet influence after the war would be restricted and domestically the tremendous cost of development would be justified.

The Atomic Bomb Would Be Used on Japan, not Germany
Soviet Decision to Enter the War against Japan
Other Reasons for Dropping the Bomb
The Potsdam Declaration
Why Did the U.S. Decide to Drop the Bomb on Japan?