Revisionist history on this topic was once a common part of anyone's education. Now it seems that this subject is no longer discussed in any detail, and that is a tragedy because there is so much learn from an detailed examination of this day in world history.
Severance does an incredible job in ferreting out the debate before the bomb, among Truman's advisers, the military rationale, and more. The detail makes for fascinating reading. What he shows is that the bomb was not necessary for military reasons. The war was effectively over, and Japan was ready for surrender. Many people pleaded with Truman not to go ahead. Nor was it recommended by military specialists. He then examines Truman's motives and concludes that was really at stake were US interests in rebuilding Europe. It was a statement of power. You can agree or disagree with the author as to whether or not this is a good thing and worth the lives of innocents, but either way, you will be impressed by his research.