Alex WellersteinVerified account

(Truman's personal role in the bomb decision, per General Groves, was "one of noninterference—basically, a decision not to upset the existing plans." He was told many of the plans, but it's not clear he totally understood them, or the details. Again, he had a lot on his plate.)

(The idea that Truman "decided" to use the bombs is an after-the-fact story that Truman and others liked to tell, to make the use of the bombs seem more deliberated over than it was. Many other people made decisions, but Truman himself participated in very few of them.)

Separately, most Japanese archival evidence shows that the Nagasaki bombing did not materially have an effect on the Japanese high command, either. They learned about it during a meeting they were having to discuss Hiroshima and the Soviet invasion.

This was the same meeting where they decided to put forward an offer of conditional surrender (which the US rejected). There isn't any evidence that the Nagasaki attack changed anyone's point of view in that room.

Absence of evidence is not absence of effect, but it clearly wasn't a crucial part of it. The idea that the Japanese didn't believe that the US had more atomic bombs is mostly untrue. If Nagasaki hadn't happened, it seems likely that little would have changed regarding surrender.

This is why many people who have studied it have found Nagasaki not that justifiable. Ted Telford, the chief US prosecutor at Nuremberg, concluded that had had "never heard a plausible justification of Nagasaki."

I think one can come up with "plausible justifications" for Hiroshima, even if they are debatable. Nagasaki is definitely a trickier moral issue, if your concern is with not slaughtering masses of civilians unnecessarily.

(If your argument is, "the Japanese [people] were evil and deserved it," then clearly the issue of plausible justification isn't an issue for you. I always get many replies to this effect.)