This may not make much sense, and please don't say "The Depression was OTL!", but I've been playing the Kaiserreich mod for HOI2, and I can't help but think about what a sad, broken world it must be. It stretches implausibility on the surface, but I think it's onto something actually fairly interesting, namely the economic aftermath of a Western Collapse in the Great War.
Essentially, what would the ramifications be for a revolution in France and Britain in the aftermath of the Great War? Or even their defeat? It seems to me that a German victory in the Great War would smash the global economic order far beyond OTL, since Britain was still a major lender and investor overseas even after the war.
Does America fill that role earlier? Germany seems unlikely to step into the role, since even if they win it'll be a near run thing...