(Just an idea I thought about; here's just a basic intro. feel free to add ideas and comment!)
From the 12th century all the way to the 13th century, the Mongols would remain the undisputed dominant power and rulers of their unified China--only to be replaced by yet another nomadic barbarian tribe from beyond the great wall 300 years later: the Manchu, a rugged and fearsome Siberian people, and the arch-nemesis of the Han-Chinese.
The Manchu would be the rulers of the Chinese people and China from 1644 - 1911 (fact) but in this alternative timeline, the Manchu would only rule over the Chinese for about 90 years. Because starting 1734, the West led by Great Britain begins colonizing China and creating a new world for the Chinese in which the major Western power alliances; white men, are the ruling class in China. The British royal family and men from other Western nations royalty and the royal Qing dynasty women will create a new hybrid race dynasty.