Currently my idea involves US non-entry into the war. The 1918 Spring Offensive fails as in OTL, however the fact that it failed against the Entente troops that Germany had been fighting against the whole war (rather than Entente troops
and US soldiers), and the added resources gained from Brest-Litovsk seemed to have done nothing, it's going to lead to a major morale dip for the German troops.
The Entente don't have the men to launch a major offensive as it would simply leave the lines frightfully exposed. So it really comes down to, "who will collapse first" France or Germany. It turns out to be Germany, where political and social tensions erupt after the collapse of AH.
Troops are called away from the front line to deal with rioters, revolutionaries and attempted seccessions. The Entente see an oppertunity and launch their own, pretty badly thought out offensive to try and push through to the Rhine. It suprisngly works, though mainly due to the exhausted German troops surrendering as soon as they can.
Without the US in the war, negotiations over what to do with Germany are between Britain and France. Lloyd George is in favour of carving up Germany as OTL and the same level of reperations. Clemencau however is even worse than rl, demanding the economic occupation of the Ruhr, East Prussia to go to Poland, much harsher reperations and maybe even the creation of a South Germany (Bavaria and Baden-Württemberg).
This leads to French suspicions that the British are more concerned with returning Germany to normality as prosperous Great Power that can be traded with for huge amounts of cash, rather than removing France's greatest threat.
France tries to create a more independent foreign policy based around various alliances and pacts with Germany's neighbours (Little Entente on steroids). Britain see's this as a threat, the traditional fear of one nation being too powerful on the continent. As with any other period in history, the British policy towards Europe is to try to and prevent French hegemony.
And that's how you get the split