The road to the bomb
Between 1942 and 1945, the Americans had been involved in a strategic bombing campaign in Japan. Precision bombing was not very successful. In the last seven months of the campaign, they switched to 'fire bombing'. 67 Japanese cities were destroyed, up to 500,000 people were killed and 5 million were left homeless.
In July 1945, the war in the Pacific was still going slowly. Fighting between the Japanese and Allies was fierce. Japan prepared to fight an invasion with a build-up of millions of troops and the Americans feared that invading Japan would cost them a million casualties and drag the war well into 1946.
The American President Truman did not want the Soviet Union to get involved in the Far East. They had used the war to gain control of eastern Europe, and Truman did not want the same thing to happen in the Far East.