The Persians came from a similar area in central asia as did the Ottomans/Turks. The Slavs were so incompetent as fighters they gave the world the name SLAVE.
Firstly, the Persians along with some Afghans were not originally Central Asian, they are Indo-Aryan. The Turks and practically all Central Asians are from the Altaic Family. Your statement makes it sound as if they were the same people which is anything but true.
I do agree with you in that not enough attention has been given to Central Asian Civilizations but the same could also said about African, South East Asian and more. The most obvious ones to me are the Abyssinians and the Jews, both have rich and long histories. The part about Slavs doesnt seem right, the Ottoman Turks fought against the Serbs who are Slavs and the battles were terribly fierce. Later when the Serbs became part of the Ottoman Empire, they fought along side with the Ottomans. Once such battle was against Timur-Lenk in 1402, Yildirim (Thunderbolt) Sultan Bayezid army was all but broken and fleeing except the Janissaries and Serbs, they fought heroically side by side until the end when they finally succumbed to the assaults of Timur-Lenks army.
Finally, Turks and Arabs. They do share the same religion, many of their cultural aspects are the same, however they speak different language, originate from different place, and both have a unique and different history from one another. If you classify them as the same, then apply this to others and you would be left with on Civilization in Europe (EC Civ

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oh yeah, the Koreans (that was what this thread was about

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sure they should belong on the game, why not? I don't mind more options for people, heck if you had 30 more Civilizations in the game why not? Yes you would get some Civs almost identical to others, but you can select who you want to play against and who you dont... if it makes people happy I am all for it!