There are many factors in the eventual downfall of the Germans in WWII but I am surprised that no one has mentioned the capture of an Enigma cipher machine.

I voted for Perl Harbor, it really brought the American citizens support into the war effort and not just the armed forces.

My 2 cents…
I think that WWII was the last time that Americans used the volume of troops to win a war. We thru so many cheep Sherman tanks at the Germans I am surprised they lasted as long as they did. The Germans definitely had a better military, veteran troops, superior equipment, ships/u-boats, etc. but they just had too many enemies. Basically the world minus Japan, who really didn’t help them much if at all.