There has been a long time argument on why the atomic bomb was used to defeat Japan. The threat of Russian progression in Europe and in Asia was enough to worry the top officials in the United States and British governments. The about to happen 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 progression. .
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 plans 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 they had not only soldiers to fight against but also the citizens of Japan loyal to their emperor? Massive destruction, immense loss of life, and putting off of the war until late 1946 would result from invading on foot instead of using the bomb. .
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Revenge also played a role in the decision to bomb Japan. The Japanese were not following the Geneva Convention in regards to care 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. The Japanese gave no warning to the Americans and no war was declared until after the incident.
The Russian territorial growth definitely played a factor in the dropping the bomb.