While France wasn’t crushed by the Germans in WWI like they were in WWII, major parts of the country were under German control. In 1917 the Russian Revolution and their peace agreement with Germany meant the Germans got massive reinforcements for the Western Front. It is certainly arguable that the French would have collapsed without the stiffening of the lines the American forces allowed.
Yes I know!
I wrote a previous FR post about the French Army mutiny of 1917. Pointing out this occurred after Verdun, Somme & 2nd Battle of the Aisne & that the Aisne battle was the breaking point. The thing that kind of help hold things together for the French Army was Petain’s leadership (yes him!) and the anticipation of the US entry. If we had stayed out, in my opinion the French Army would have collapsed and their would have likely been a negotiated settlement. I doubt if the British could have stopped it or even had the internal (by that date!) political will to try. It would have left Imperial Germany dominant on the continent but with a Social Revolutionary to Bolshevik Russia at their east. Might have been a better result for Europe & the world. Read the book “Myths of WWI” has some interesting & surprising commentary on all the participating armies.