For America,only Maya and maybe another Native tribe are worth to add.
For Africa,Carthage,Kongo,Ethiopia and Nubia are worth to be added.
The civ must be historically "important" to be added.
Are you kidding me?
For starters, I wouldn't call Carthage worthy (I've gone into this before, though, so I won't digress too much here).
For the Americas, many large-scale, advanced civilizations lived there before the Europeans showed up. And most of Europe's success in colonizing came from disease and native alliances, to boot.
I may not know as much about Africa's history, but I know many early civilizations existed there, as well.
Besides, I also would think some former colonies could qualify, as well (Brazil and South Africa are mentioned relatively frequently, and I personally think Brazil would be cool).
I'd be careful about what you call a "tribe" (the Zapotec, for example, were not a "tribe", they were a civilization), and where you go with "historically important". Just because they weren't important to Europe, doesn't make them unsignificant.