Well, you get into various topic. Let me begin at the backside with a few quick sentences:
1. Splitting of nations (Civil Wars, etc.) have been proposed already and discussed various times in other threads. It would make no sense to list up all the things there said in here.
2. The UN: It's the same thing as with splitting of nations: Other threads exist. But I personally do not approve of this idea. It's just too complicated I think.
3a. When we take your scheme as official to chose the civs, some 'civs' from South America do approve. Argentinia for example had a big impact in history (f.e. Falkland Wars), culture (f.e. Evita Perron aka Madonna...

), science (f.e. Che Guevara was Argentinian). Ok, these reasons are a bit obscure, but they certainly are as good as a nation as Portugal or the Netherlands, who also were chosen. Then we go with Brazil. I could again list many reasons, but I think you can imagine what I would write. Another last candidate from South America would be the Andes-states, the idea of Simon Bolivar. But I don't approve to this idea, because it would be ahistorical. Then, I haven't talked of cuba, ....
3b. Europe: What about the Magyars (maybe Austria-Hungary?) or Poland. I accept that you think Serbia isn't worth. But these two 'civs' are certainly worth including.
3c. Africa. What about South africa. No impact on history. I beg your pardon, they are equally important as the USA, just from a different point of view (apartheid, 'boers' (boer-wars), diamants, etc.). What about Mali, Songhai, Abyssinia. These were never occupied by Europeans. I could go on.
4. My two euro-cents to your scheme. It's a good one, but you gotta take the global view by chosing their importance. Imagine you were a trade in arabian Baghdad in the first half of the last millenium (1000-1500 AD). What would your point of view be? You would know less of America, but more of Africa and Asia than you do as a European.
The problem is that we get teached history from a Western point of view and therefore we are too much concentrated on this, and argumentations as yours above develop.
mfG mitsho