How can you make it so that, with a POD between 1400 and 1900, China is split into two culturally separate nation-states, of comparable size and/or power, to modern day, and with little desire to reunify?
It's just possible that a KMT victory at Huaihai and a CPC victory at Tianjin *and* an escalating Cold War leads to a Korea-style partition of China. North China becomes a psychotic and totalitarian dictatorship, while South China transforms from a corrupt and semi-fascist military dictatorship to a rather conservative and corporatist democracy and an economic powerhouse.
Both Chinas profess the goal of reunification, but the insanity and backwardness of the North make many young South Chinese balk.
No that wouldn't even rate in the top ten splits in Chinese history.
By the Ming dynasty in 1400 it's way too late, China as a whole have more or less accepted the Confucian illiterate-civil service tradition/system as a binding force for itself. In other words, the ties of language, high culture, and the prestige of the "all under heaven" imperial system is far too ingrained in the social and political elite of the time for it to be broken.