A few issues that have not been brought up here:
The USA did not know for sure that the bombs would work. True, they had tested them and found them to work, but the reality was that they had only a few bombs made and they were left with a situation where they could announce to the world we are going to drop the bomb on some island and then it was a dud. Or they could bomb the chosen city without announcement and let the results speak for themselves.
The United States had an effective blockade of Japan and could have chosen a path of starving the enemy into submission. Japan had strong peace negotiations with the Russians and a good blockade could have accomplished the same result of the ending of the war. As previously mentioned in this thread, the USA also had issues with other Allies in the war they were addressing with the bomb's use. A blockade certainly did not have the same impact as everyone in world seeing firsthand the macdaddy weapon we possessed in action.
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