Even Fritz Fischer’s book on German war aims in WWI (which is in no way complimentary to Germany) admits that they entered the war with no war aims. The reason for the attempted “knockout blow” in the west was because the German High Command felt that they could not win a protracted 2 front war and that the best bet was to defeat France before Russia could mobilize. Russia mobilized faster than expected, though.
Without American interference in 1917 the Central Powers had the war basically won when Russia surrendered. There was no way for Britain, France, and Italy to deal with Germany, Austria-Hungary, and Turkey at that point. France faced the trench mutinies in 1917, and Italy was on the brink of collapse. A negotiated peace at that point would probably have spared us the movements that brought about WWII - and possibly the Bolshevik Revolution later in 1917 as well.