I don't think it's such a bad idea to have a couple different "lines" of government that evolve. An authoritative one, a religious one, a democratic one, and a populist one, for example.
For example, at the beginning of the game, before the existence of official governments, you could have:
Authoritative: Warlord
Religious: Shaman
Democratic: Tribalist
Populist: Chiefdom
Which, by the middle ages, becomes:
Authoritative: Despotism
Religious: Theocracy
Democratic: Feudalism
Populist: Monarchy
Which, by the modern ages, becomes:
Authoritative: Fascist
Religious: Fundamentalist
Democratic: Democracy
Populist: Communist
... note -- the categories and examples I pulled out were the first that came to mind, and they're not refined. I was more just expanding on Krikkitone's ideas. "Food for thought".
And, assuming it's a good idea in the first place, you'd find a better list of governments from a few other people, let alone Firaxis.