The reason this is special is because no one else used a nuclear bomb, before this event or after. That's basically the definition of "special" and the number of Chinese that the Japanese killed has nothing to do with it.

Picking anything other than the nuclear bomb to never happen again is moronic because the planet can survive the other things, but if nukes were to start flying again, it would most likely not end with just two. Other countries have those weapons now too and such a war has the potential to be last one ever fought.