I don't really understand some of the civilisation choices. No offence to Tomatekh, these may be the most polished civs I've seen in some time. I understand Goths, Sumer, Garamantes and Hittites, and maybe Benin - good choices there. But the others? Kievan Rus' were the ancestors of Russia if I recall correctly, so why not simply play as Russia? The Timurids, well, I'm assuming you are referring to Tamerlane (sp.?) who was a Mongol. Mali, well, it's the same thing as the Songhai surely?
The Timurids weren’t just Mongols and weren’t just Persians. They represent a merging of those two cultural-lineages that really created a unique culture and atmosphere that significantly changed the cultural-milieu of that area from then on. They did carry on aspects of both cultures, though, becoming the center of Islamic learning for a time and keeping elements of Mongolian administration. However, they also created new forms of art and architecture and really were a melting-pot culture from influences along the Silk Road. The Safavids that conquered the Timurids were really
the Persian culture and were the ones to re-establish Persian-Iranian identity in the area after the Timurids fell. It’s also hard to say the Timurids were just Persian or just Mongol when the part of them that wasn’t conquered by the Safavids essentially became the Mughal Empire which became one of the major empires and influences in India.
Mali and Songhai are a case of geographic overlap; however, they represent two different cultural groups and kingdoms that conquered the same area rather than a single empire under different dynasties. Mali grew from the Kingdom of Nyeni of the Mandinka ethnic group and spoke Mandinkan. Songhai grew from the Kingdom of Gao from the Songhai ethnic group and spoke Songhai (Mandinkan is a Niger-Congo language while Songhai is a Nilo-Saharan language). There is overlap between the two in that both adopted Islam and Islamic culture and they both conquered many of the same kingdoms, but they weren’t the same empire. If this was Europe, and two separate kingdoms (with different languages and cultures) conquered each other’s land, I kind of feel the question of their difference wouldn't even come up?
I don’t really want to say anything about Kievan Rus’ because if I do, it’s going to make someone angry and they’ll fill this thread with angry comments like I get on the Steam Workshop. But, essentially, the history of Russia proper begins with the Duchy of Moscow after it gained independence from the Golden Horde. It then claimed translatio imperii both of Kievan Rus and Rome (through a marriage with the niece of the Byzantine Empire). Kievan Rus’ was really its own unique state, though. It was a collection of principalities that were briefly united under the reigns of Vladimir and Yaroslav. After which, the central authority began to break down before the whole thing was conquered by the Golden Horde. It was a predecessor state to Russia but it doesn’t really have the same direct, unbroken lineage that you can see with the Duchy of Moscow, to the Tsardom of Russia, to the Russian Empire, etc.. However, more than the other two, this civ can be argued either way depending on how you personally draw the line for civs. Then again, it’s also similar to how Civ IV included both the Holy Roman Empire and Germany.
(I'll also say, Kievan Rus' is one of my most popular civs).
Besides, you can technically argue that the Byzantine Empire was just the Roman Empire. Why make them into a separate faction? Or the reverse of that, the “Polynesian Empire” in the game really represents two distinct cultural groups and several independent kingdoms that never interacted with each other. Why make them just one faction?
And partly, I just make the factions I find interesting, and I also think the historical importance of those three factions justifies their inclusion over any potential overlap.