When it comes to dropping the bomb twice on Japan, the people making the decisions and those advising them knew exactly what they were doing. Japan was already defeated and everyone knew it. The selection of civilian targets and especially the decision to drop the second bomb was known to be completely unnecessary with respect to Japan. It is hard to think of them as anything but atrocities perpetuated by people who know exactly what they were doing, the difficulty being that even if they were only done for political strategy they might have been entirely necessary to prevent something much more disastrous than WWII.
The reasons those bombs were dropped were to scare the fuck out of Stalin and keep his armies away from Japan. Perhaps unstated, but pretty obviously so. There are so many ways the world could have been very much worse after WWII, all in all it went very well (despite what many people think).
As for the testing there were people actively protesting it's beginning and continuation, but the effects and persistence of effects were not fully understood for some time. That is what you're getting at it seems. It wasn't so much about the world being a different place but that the consequences of radiation being unknown.
I won't pretend to know what was in the minds of the people at the time. Maybe there were multiple reasons and not one single "real reason."
Looking at the world today I think most people would prefer that a device that can cause such massive destruction simply not exist. I can only imagine what will happen once the ones that have been 'lost' start showing up in the wrong hands. The destruction was bad enough when in the 'right hands' (scare quotes, because I don't feel so great about what we(USA) did either.)
We can play what-if all day but we will never know what would have happened if things didn't happen as they did. I just hope that the actual version of what happened doesn't get 'corrected' in history books so that our future descendants can learn from our mistakes.
Unfortunately the bomb is obvious. It is not some eldritch construction which could be forgotten and lost forever without great effort to recreate. Once you have developed atomic physics the idea of a bomb is inevitable and once you know it can be done building one is trivial requiring only mundane resources (but a lot of them). You could explain how to build one to a child.
Increasing power is a consequence of expanding knowledge.
- Adm. William Leahy (President Truman’s Chief of Staff)
- Henry Arnold (US Army Air Forces commanding general)
- Adm. Chester Nimitz (Commander in Chief of the Pacific Fleet)
- Maj. Gen. Curtis LeMay, (head Bomber Command)
- Gen. Dwight Eisenhower
are all on record as acknowledging that "Japan was already defeated". [1]
[2] Japan knew they could not win and were concentrating on obtaining the best possible terms of surrender, hoping that Stalin might be convinced to mediate a settlement between the United States and Japan.
This hope was dashed by the Soviet declaration of war and invasion of Manchuria and Sakhalin Island, which happened at 1 minute past midnight on August 9, 1945 [3].
Another important factor is that Japan had good reason to be wary of USSR military might [4].
It's arguable that Japan's fear of fighting the USSR is the reason Japan went east (to Pearl Harbour) instead of west (to eurasia) in Dec. 1941 [5].
[2] and [5] are thoroughly researched and make compelling arguments.
The reasons those bombs were dropped were to scare the fuck out of Stalin and keep his armies away from Japan. Perhaps unstated, but pretty obviously so. There are so many ways the world could have been very much worse after WWII, all in all it went very well (despite what many people think).
As for the testing there were people actively protesting it's beginning and continuation, but the effects and persistence of effects were not fully understood for some time. That is what you're getting at it seems. It wasn't so much about the world being a different place but that the consequences of radiation being unknown.