I have divided Germany into five countries, not three:I'm not sure Central Germany would be stable. The Saar is wealthy and a tempting french target. In OTL they weren't super happy about not being able to keep it in the aftermath of WW2. Otoh the separate Saar dialect is as much a product of post WWI history as anything else. Further, Thuringia skews Lutheran, while Franconia skews Catholic, and the Rheinland-Hesse regions are split too. The region is united by language, but that's about it.
- Saxony
- Fraconia
- Thuringia
- Alemannia
- Bavaria
I have ignored both the East Low German and the North Upper German speaking regions. Former will be part of Saxony and later will most likely be divided between its four neighbours.
And the PoD will be during the medieval age.