Everyone who speaks Greek is civilised, every one else is a barbarian (because when they talk they just go 'bar bar bar'). End of discussion.
As for the US ingame, I think only a PC game starting with the Revoloution, and focused specificaly on the US political structure and situation etc etc could evr really provide a realistic outcome. In game, an EU/ Rome style colonisation would probably be good enough, though one would need to ensure that it is hard for anyone else to take it first, even though many did or had claims (Mexico, British/Canadian claims etc.)
Maybe a pop migration rule which allows pops to move themselves into the area, establish themselves then fire an event to become a part of the union?
What ever the case, something needs to prevent the rapid colonization of the entire US, and also one which maybe allows the player to persue a Jeffersonian America.
But as I said at the beggining, modeling the 19th C USA will never be an easy task.
Well, no, I was thinking more along the lines of a civilization being one that depended upon agriculture, had a transportation system, had long-distance trade, writing, standards of measurements, art, math, astronomy, architecture, and some sort of legal system. And I guess it does actually matter since you can annex uncivilized nations outright.