So, we can actually make new but plausible nations, right?
How about the Carpathian Federation?

It'd either born after 1849 when the various revolutions in the Austrian Empire succeeds.
Or it'd be formed after WW1. The allies realize that the League of Nations is a bad idea and instead they promote a federal system and actively ban the Habsburgs or any royal figure from interfering with it. Potentially this would mean that the friction between various nationalities would be less otherwise there's no way it could work.

Also I can understand that you wish to start this game when USA is involved, too.
But that'd practically prohibit people from exploring plots from earlier times.
For example my Carpathian Federation would most likely interfere during the Polish Invasion already.