What did Hitler ever do to us?
He declared war on us.
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Taking the longview, yes, if we had stayed out of WWI - at the time called "The War for Civilization" - then that war probably would have ended in stalemate. There would not have been the humiliation of Germany at
Versailles. The ground would not have been sown with
dragon's teeth. The nightmare of the Third Reich and the subsequent annihilation of European Jewry could have been avoided.
This observation does NOT absolve
Hitler's willing executioners of the guilt for their actions. It's just an observation of how the policies of nation states influence the flow of history.
In other words, a policy of nonintervention would have been far superior.
Wars don't end in stalemate. They can't. "End" and "stallemate" are mutually exlcusive.
When a war ends, one side notably victorious over the other. When neither side can attain a victory, the war doesn't end. It simply festers for a while, until it flares up again at some future time.
The modern fascination with UN-brokered cease-fires, negotiated peace settlements, and so forth is folly. These sorts of deals never end wars, they simply punt them off into the future, where presumably they will be some other politicians' problem.
Anyway, regarding US intervention in WWI... US nonintervention would not have resulted in a stalemate. Both sides would have continued to fight until one side was demosntrably defeated, or the hostilities would have gone dormant for a time only to flare up again in the future.
One could even argue that Germany wasn't truly defeated in WWI, in the sense that the west never destroyed Germany's will to fight. The Versailles Treaty, despite being tough on Germany, was probably premature. All it did was give Germany a breathing spell in which to re-arm and re-equip, thereby allowing her to re-open hostilities a few years later from a position of much greater strength.