All this talk of major/minor civilizations... I don't think it's quite proper. Instead, let there be a great number of civilizations (I will make a list later). All would start out in a tribal organization, and would always have a chance to settle down. As a tribal organization, the tribe's population could not grow quite so rapidly, and could make raids on cities. These tribes would be like units with population, a settler/raider unit. This unit could make a boat if near forest and ocean. (This I say because many peoples in history made folk movements by boat, ie the sea peoples of the mediterranean.) Of course, in order to stay succesful, all tribes would have to settle down (no technological progress could be had.) I like this idea of a tribal system because there are many nomadic tribes across the world today, and it does not respect their culture by having them be in cities.
I have read of an idea of flags. I really like this idea, particularly if it let you design your own flag, and/or choose from historical flags related to that particular tribe/people.
Enough of my incoherent ranting, here's that list!
(Non-alphabetical, because I'm a lazy bastard.)
Australian aborigines
Polynesians
Melanesians
Koreans
Japanese
Chinese
Mongolians
Huns
Uighur
Tibetans
Turks (not of Turkey, but of Central Asia)
Thracians
Scythians
Illyrians
Babylonians
Sumerians
Indus Valley/Indian
Khmer
Ainu
Inuit
Arabs
Hebrews
Phoenicians/Carthaginians
Egyptians
Cu****es/Nubians
Numidian/Berber
Basque/Iberians
Celts
Romans
Greeks
Slavs
Finno-Uguric peoples
Norse
German
Taureg
Shona
Zulu
San/K'ung (aka Bushmen)
Mali
Ethiopians
Massai
Nok
Kongo
Tupia-Guarani/Amazonians
Quechua-Aymara/Incas
Mayans
Aztec
Anasazi
Pomo
Lakota (aka Sioux)
Iroquios
Seminole
Taino
Beothuk
Cree
Ottowa
[Can't think of any Pacific-Northwest tribes]
Explanation for lack of Americans:
Having the Americans, descendents of English, Irish, Scottish, German, Dutch, Welsh, French and other Europeans who owned African and Native American slaves start with early technologies alongside such cultures as the Sumerians and Nok and China is, in my mind, not the best idea...
Have fun yelling at me.