Hi there -- you may be interested in this section of our FAQ on the atomic bombings. The brief answer is that in popular culture, we have an idea that there was some sort of affirmative decision made (by Truman) where they wrestled with e.g. casualties caused by the bombing versus the cost of an invasion. It didn't happen like that -- while Truman made a decision to stop bombings without his express consent after Nagasaki, there was no decision taken to start bombing in that manner. It was more of a case of "we're building this weapon, we will use it." u/restricteddata explains this much more eloquently in the linked answers.