Well you can't really raise taxes, so Communist Russia be an authoritarian government with collectivist and the lowest living standards available, I think collectivist has blocked off the lowest one which in this context is a little innacurate.

Federation is just a form of democrazy.

Understanding historical governments I think comes down to just understanding 4 basic aspects of a government.

conservative/progressive
authoritarian/egalitarian
libertarian/elitist
collectivist/individualist

Maybe it's
Authoritarian/libertarian
egalitarian/elitist

There are nuances though, in this mod and vanilla game there is no conservative/progressive.
Also collectivist isto a lesser degree also conflicting with libertarian.

I think most historical governments can be understood as a combination of those.

A wiki article on each country should give you broad brushstroke ideas about the particular nation.