So there are a few Central Powers win WWI going on right now, so I thought I'd throw this into the ring, see if there are any takers.
I'm of the belief that even if the Americans didn't intervene in WWI, the Entente would still win the war, perhaps even more completely then OTL. IMO the Germans could not take Paris in the '18 offensives due to insurmountable logistical hurtles, hurtles that even sans the Americans would still be in place. Once those offensives fail in '18 its pretty much game over for the Germans. The Austrians are falling apart, the Ottomans have lost control over most of the Arab parts of their Empire, and the Entente has started its own successful offensive operations.
So what does the end of the war look like? The Germans know they are no longer capable of launching another offensive, but at the same time the Entente is also bled nearly white.
I think the war would proceed as follows, but I want others input.
Without the Americans involved however, the German leadership may not see the game as up. In OTL after the '18 offensives failed the Germans knew that the Americans were only going to come in greater and greater numbers, and decided to call it quits while they still occupied northern France. In this TL the Americans are not involved (and thus Wilson and his somewhat attractive 14 points are out of the game) and the Germans may believe that the Entente is just as close to internal collapse as they (the Germans) are. Therefore if they can just hold out a little longer . . .
The orderly retreats of '18 turn into routs in '19. Word of worsening domestic conditions, rumors of rejected cease-fires, and the withdrawal of troops to deal with the "Austrian Situation" destroys German morale. In April of '19 the Germans ask for a cease-fire. The Kiel Revolt happens as per OTL, and Germany is gripped by civil war.
Meanwhile the Allies decide to make a peace that General Foch would really approve of. I don't know what all the details are, but much higher reparations, and French annexation of the left-bank of the Rhine feature prominently. With Germany gripped by civil war the Germans are forced to sign the treaty.
Couple of questions:
Do you think that the Entente would force the Kaiser to abdicate, or was that a pet peeve of Wilson?
What does the Balkans look like?
Whither the Ottoman Empire?
Is it possible that a harsher peace, combined with a more complete German defeat (that's what the point of this scenario is) would make for a more peaceful world (ie, Versailles is not a 20 year cease-fire, but the end of intra-Western European warfare)?