Lets say the Germans play out their 1918 offensives better, get close enough to Amiens to put it under artillery bombardment limiting Allied movement, the other offensives go a little better but are not decisive (perhaps Reims falls). However the Allies can't launch any offensives in Palestine, Italy or Salonika in 1918 due to the need to reinforce France and can't counter attack in the western front until 1919.
The Allies continue to build their air forces, build tanks, bring in more Americans, lay their anti submarine minefields etc. so that a combined July 1919 offensive on all of Western, Italian, Palestine and Salonika crushes all Central powers resistance so that by November 1919 the Allies are across the Rhine, Bulgaria Austria and Turkey are out.
Germany requests an armistice one year later then OTL.
What are the effects going forward of
a) A greater German defeat on the western front (lets say major organized resistance is crushed)
b) Greater American involvement than at the end of the war OTL
c) Greater use of tanks in 1919
d) Greater use of strategic air in 1919
e) More complete defeat of uboats in 1919
f) The defeat of an even more ragged Austria (one year later than OTL)
g) A one year longer German occupation of Russian regions