...and yet, none of them had the bomb to drop on anyone else. Literally a case of a bomb in hand is worth infinite (unrealized) in the bush. Realpolitik runs on what you can do now.
What do you not understand about the human condition?
We are energy/cost optimizers. We want to achieve resolutions of conflict as cheap, and as quickly as possible, i.e. with minimal cost.
We made a bomb. Arguably the biggest bomb there had been any indication of anyone having gotten working before.
Truman was looking at war projections of costs to invade Japan. Then he got the papers that said we could make an entire city disappear with 1 plane, and one bomb.
Do you really think it would have worked out any different for anyone else?
I say: No. It wouldn't have, because using it as soon as you got it is just human nature.
How much differently do you think things would have gone if Japan was also a nuclear state at the time?
I'd seriously reconsider the logic pf your position.