And have you thought about how many potential hitlers were pruned in the WW2 ... every one that died in the conflict could be much worse than him. So maybe Hitler was a historical fuse. A maniac just 20 years later could have destroyed humanity. Dead serious here, assume that nuclear weapons were available from day1.
So maybe there was time travel manipulation to ensure WWII so that humanity could survive.
Perhaps the WW2 in our timeline is the least worst outcome.... :-|
e.g. What if the Normandy landings had failed? The Nazis would still have been defeated by the Soviets but the whole of Europe north of the Alps could have been occupied by the Soviets, perhaps making a far worse later nuclear conflict much more likely.
So maybe there was time travel manipulation to ensure WWII so that humanity could survive.