Ethnically I think it would even subdivide further then this map shows.
I disagree, in the exact opposite direction. I believe that China is 91% Han Chinese... ad Taiwan is 95% Han.
BTW: On mainland China, they tend to treat non-Han Chinese pretty poorly... but not as bad as blacks or Japanese.
(But American whites are somehow the only racists on earth)
Ethnically I think it would even subdivide further then this map shows.
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I read somewhere years ago that different languages were often spoken from one valley to the next, around 4000 the article or book said. That is why Mandarin is the official language of China. Seems possible that you are right.