Actually...the main purpose of this thread is to examine the ATL WWII and 1930s/1940s, so for the sake of the discussion, let's assume that the WWI proceed pretty much like OTL, including the Treaty of Versailles.
In regard to Germany, *maybe* the Harzburg Front managed to mount a succesful united front. The Deutschnationale Volkspartei formaly associate themselves with the
Stahlhelm and end up taking the place of the Nazi in this timeline.
Another possibility is a complete military takeover of the republic by the prussian faction of the army with the excuse of "stabilizing" a "decadent" democracy.
Lastly, though a long shot considering the atmosphere at the time, the left hold on to power.