There has been a long standing debate on why the atomic bomb was used to defeat Japan. The threat of Russian advancement in Europe and in Asia was enough to worry the top officials in the United States and British governments. Wherever the Russians moved through they took for themselves. The imminent invasion of mainland Japan and the allied casualties that came with it were also a factor in the decision to drop the bomb, as said in document A. The dropping of the bomb was not entirely used to stop the Russian advancement.
If the allied forces had invaded mainland Japan, many lives on both sides would have been lost. Most probably more than were lost in the bombing of Hiroshima and Nagasaki put together. The tactics that the allies had used up to this point had cost hundreds of thousands of lives on both sides. This was when the Japanese only had maybe two or three thousand men on an island; whereas on the mainland millions of people who would fight until their death to protect their country.
Can you imagine if the Americans invaded mainland Japan where hey had not only soldiers to fight against but the citizens of Japan loyal to Hirohito? Massive destruction, immense loss of life, and prolonging of the war until late 1946, as stated in document A, would result from invading on foot instead of using the bomb. Revenge also played a role in the decision to bomb Japan. The Japanese were not following the Geneva convention in regards to treatment of prisoners of war.
Which says that the prisoners are not to be put through torture of the psychological or physical nature. The Japanese did these things anyway, they would decapitate American prisoners, or they would shove bamboo shoots under their fingernails. The American government also wanted revenge for the surprise attack on Pearl Harbor. No warning was given by the Japanese to the Americans and no war was declared until after the incident. The Russian territorial expansion definitely played a factor in the dropping the bomb on Japan.
The Soviet Union had already taken Poland and many other countries during the war. The Soviets were helping the Chinese with the war against Japan and later would get railroads in China and Manchuria when Japan completely surrendered, as stated in document D. As said in document E, the Americans did not want the Russians to get involved in the war against Japan. The most obvious reasons would be to prevent the Russians from expanding any more and to keep them out of Japan where they would hamper the peace process and gain even more territory.
As president Harry Truman says in his radio address, document H, all of he countries involved were trying to create the atomic bomb to use for their efforts. Fortunately the Americans won the “race of discovery”. If the Germans had won that race they probably would have used it continuously in Russia and Britain until Hitler got what he wanted which was world domination and the extinguishing of the Jewish and others and the ascent of his “superior race” of Germans. The dropping of the atomic weapon on Japan was not entirely to halt Soviet expansion although it did play a major role.