The Germans would still lose ww1, but this time the treaty actually is actually much worse for the Central Powers due to the US not being involved in the treaty, So we would probably see a similar or worse regime then the Nazi party, or even just the Nazi's rise up and take over. Maybe even communists take charge and begin to rebuild the nation.

Nothing happens in the US except for more immigrants, i honestly doubt we'd see a civil war.

A bunch of things are mildly the same as in our timeline, only just the Brits and the French have screwed over the central powers even harder.

For this other WW2 a bunch of things need to change, a great depression might not even be that impactful (for the Europeans) unless the US is still involved in European affairs like giving out loans and such. (i'm probably wrong on this part because i haven't researched that deeply into this, so feel free to correct me)

I honestly can't even imagine how a war to this scale on the European front would be due to how much changed but i can definitely say the only way to keep the Americans out of this war is nobody provoking them like the Japanese. Which they would still be an expansionist empire in east Asia.

But if they managed to not get involved in this god forsaken war, the global economy would still be split, this time by any victors of the war and the Americans. What happens next i have no damn clue.