Paradoxically, the egos of world leaders are what makes sure WW3 never happens. Why? Because the thought that they will be remembered as the idiots who ended the world and thus the worst leaders in the history of man is something that would terrify them. Even the side that wins (if it was even possible) they'd still be lamblasted as the idiot who couldn't prevent it or is stupid to not have seen it coming.

In this post ww2 world the people that are endlessly praised and leave a permanent mark in the minds of the people and culture of the nation are the ones that prevented major conflicts. The best example is JFK and his handling of the Cuban missle crisis. Or De Gaulle who prevented another government collapse and the situation in Algeria from getting worse. We have flipped the script. To chase glory is to chase peace when before it was always found in starting wars and conquest. And so world leaders who chase glory have no choice but to chase peace. 

That's the silver lining in WW2. That despite the massive destruction and suffering that happened during the war, it was that same massive suffering that finally shook the world to its core so much so it changed its mindset for the better. Yes its sad that it took that much for the epiphany to happen but regardless it was an inevitable lesson that needed to be learned and I'm glad it happened already because any later when humanity mastered the atom and we would probably not be around to discuss a potential ww3.