Well you can't really say they are the same factions considering historically each of the states had their own language, writing system, currency, etc...and they each had different styles of fighting, different armors, weapons, etc.
You can always include the many kingdoms in what is now known as Southern China, and many nomadic factions in what is now known as Northern China, and plenty o Greek/Persian/Indian factions to the west.
I'm not sure if "Korean" identity existed in that time period...
Ummm, even today China is far from homogeneous...
You have disgruntled minorities living in the west and south west, and your integrated minorities in Inner Mongolia/Manchuria/Sichuan/Yunan/much of the southern regions/etc. And they've been able to retain their distinctive culture...
Their government lists 55 minority groups (about 150-200 million people)...but the real figure is probably much higher.
Remember that "China" is roughly the size of the entire continent of Europe...and the modern boundaries and conception of "China" is the result of thousands of years of conquest and integration of vastly different people.
(ie. Thai, Cambodians, Hmong, Viet, and Austronesian people all had kingdoms in Southern China before being integrated into various Chinese Dynasties)
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