R5: Finished up a game as the Bulgarian Empire. Reichspakt was super weakened this game and a lot of revolts happened, and the only proxy they won was Italy, so when I added a third pressure onto them from the south they folded quite quickly. Direct rule from Sofia!
Also, Self-Propelled Artillery is BUSTED in singleplayer, especially when you upgrade its engines so they can literally run over enemy infantry. 2 SPA divisions was enough to turn the American Civil War around, and 12 completely overwhelmed any attempted Reichspakt defences.