We’ll just read their autobiographies and written comments after the war. Ifs pretty well known if you have a modicum of basic knowledge of the time. Winston Churchill, Anthony Eden, the French leaders and the Americans who served in the diplomatic corps. Finally even the German general’s testimony was that had Hitler been challenged at anytime before Poland he would have been overthrown. That’s not speculation sport that is solid and if you have any knowledge you would have a clue.
I think the world would be better but that’s not the problem for us to solve. What is part of our responsibility is to oppose naked aggression of a weaker country by a stronger one.