In addition, many U.S. citizens wanted Truman to drop the bomb as a form of vindication against the Japanese for their brutal treatment against all Allied soldiers and prisoners. "From this perspective, the use of the new atomic bomb to force a rapid Japanese surrender seemed a logical and necessary military action. Any moral qualms.were drowned out by the universal anger at the growing body of evidence about Japanese atrocities against civilians and their brutal mistreatment of Allied prisoners" (Nuclearfiles.org).
The Japanese were known for the heinous and inhumane treatment of all Allied soldiers. The Japanese were also famous for their fanatical way of fighting until the bitter end. Mass suicide had been committed on Saipan, hundreds had died in suicidal kamikaze 'missions', and surrendering was an unthinkable option. Due to Japan's cultural belief that surrendering was dishonorable and worse than death, Japan was expected to keep on fighting until the bitter end. Truman did not wish to drag out the war any longer. Using nuclear weapons to bomb the Japanese would swiftly bring about Japanese surrender. The above reasons are considered to be why Truman made the decision to drop the atom bomb. However, some believe that the decision to test the bomb and later drop it was motivated by a desire to scare the Stalin-led Soviets, and dissuade them from taking over Europe.
Truman urged the military commander of the Manhattan Project, Gen. Groves, to guarantee that the first testing of the atomic bomb would happen before Truman's meeting with Churchill and Stalin at Potsdam. After being told by Soviet intelligence of the successful A-bomb test, Stalin urged the small Soviet atomic bomb group to work harder to compete with the Americans. The belief that Truman decided to bomb Japan in order to frighten Stalin is supported by the idea that Truman did not need to bomb both Hiroshima and Nagasaki, if what he solely wanted was to force the Japanese into surrender.