I know some would debate this, but at least as objectively as I can be as an American, WWI was the last war that didn't have "good guys and bad guys" and I agree with the OP about just how close Imperial Germany came to winning the war, and without "dirty tricks" as one might argue was used in WWII (most significantly Barbarossa).



I believe that had the US not entered WWI, there would have been either a negotiated peace or an outright German victory (more likely the former, but the latter was in the realm of possibility depending on how well the 1918 offensive would have gone). The fact is that Britain and France lacked the ability to mount an offensive without American help by late 1917, whereas the Germans were still able to do so. This is where the old HoI2/Darkest Hour mod Kaiserreich got it right: the historical 1918 offensive happened when it did because the Germans knew they had to end the war before enough American troops arrived in France. Without that time constraint, they could have used 1918 to ensure their allies were stable and attacked when they were completely ready. At best, they win the war; at worst, both sides would have been exhausted and unable to continue to the point where a negotiated peace (almost certainly favorable to Germany, if not all the Central Powers) was nearly guaranteed.



edit: Kinda emu'd by axisgeneral