Oh, I'm sorry, but this tread is making me want to smack some skulls around. And before I start up here, I'm fully aware that I'm going to draw a lot of flak for this post. That aside, I shall begin!
First off, you have to think about what actually defines a Civilization. Because of modern day politics and map-drawing, you can't POSSIBLY start naming off countries (Or states, dear Lord) and saying they should be Civs. You have to look at the people that live in those countries before you ever start saying they should be in the game... Because, chances are, they already are.
First example: Any of the modern-day Arabic nations like Pakistan, Iran, Iraq, Saudi Arabia, etc. Yeah, these ones are pretty easy, they're the Arabs. Duh. And they very much deserve to be in the game. I mean, they brought us arts, an enourmously influencial religion, and the number zero.
Austrailia, New Zealand: Yup, they're already in Civ. As the Engish. Don't believe me? Well, look back into history. Australia was founded as a British penal colony, for godsake! History lead them off into creating they own nation, but if you take a look, they still very much bear English roots.
Canada: My own home country that, as much as it would be cool to be our own Civ, falls into the same case as the Aussies. We're originally a British/French colony, and still have the roots of that heritage. And nowadays, it almost feels like we've lost cities to the Americans due to culture
Anyways, that's why Canada (And Quebec, you fall into this!) won't be a Civ.
America: God, it still peeves be off that these guys are a Civ sometimes. Okay, yes they have had a very major influence on the last 200 years, and yes, that are the worlds only remaining superpower (A fact I loathe every day) But they still started the same way that Canada did, as a series of colonies founded by European nations. BUT, I suppose that the influence they have exerted in those last 200-odd years DOES make them canditate enough... However that does not let someone like...
Texas or the other 49 states: qualify for Civ-status. And don't even get me started on Texan research speed jokes. I have far too many. Anyways, any American state is just that, and while more emphasis is placed on indivdualism of the American states then Canada's provinces, no state is anywhere close to having their own Civ.
The USSR: Okay, I really, honestly do not BELIEVE someone said this! The Union of Soviet Socialist Republics was the RUSSIANS! They just had a Communist government, that's all! It's not like you would say there should be China and the PRC! Also, places like Latvia, Lithuania, the Ukraine even Poland to an extent, could all be considered 'Russian' (and I am careful about saying that), so they get recognition that way.
Others: Almost any other nation on the map today, especially South American nations, can fit into one of the major European nations of today, really. All of South America is either Spanish or Portugese in culture, language, art, religion... Many African nations also have their political foundings from the Imperialism Age, but culturaly, are from a few major groups. I'll get to those in a sec.
So, what nations SHOULD be in Civ? Well, let's see here, shall we?
Zulu: Hell yeah, Shaka and his buddies should be here. Any nation that nearly defeats the British army at the very height of their power earns a few points in my book. That, and when you're trying to get native Africans into Civ (which you should very much try and do), the Zulu (Or Bantu as they are also called) Another Civ you could have for the Africans is the Kosian's (Which is the predominant group in South Africa, I believe) or the Afrikans themselves. But I would need to to more looking in to that.
Israel: These guys should get way more credit then they do. Depending on your beliefs, they were very much around since 4000 BC. And they are the only culture you can truly say has seen all of history. The Greeks and Turks come very close, but the Israelites have it. Also, the Israeli army was one of the best, having defeated countless armies (when God was on their side), and now, having done it again against rediculous odds against up to 5 arab nations (Yom Kipper war, Six day war, etc.) And their religion gave birth to the largest per-capita religion in the world, Christianity. So influencial? I think so.
Anyways, I cna't see the screen straight now, and my fingers hurt, so I'm going to stop now. But if I took a look though a few history books, I could probably add a few more Civs to to this. Now then let the flame war begin!