If the Chinese Civil War was the last chance for China to be divided...

If the Kuomintang had succeeded in defending the Yangtze River line and holding out during the Chinese Civil War:
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The Communist Party (occupying Manchuria, Inner Mongolia, Xinjiang, and North China—territories of the former Jin Dynasty + Xinjiang)
The Kuomintang (occupying the area south of the Yangtze River—territories of the Southern Song?)
Tibet (which was independent at the time of the Civil War, thus remaining an independent nation)
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If it had been split like this,
the regions under Kuomintang rule would still be the most prosperous areas in China today... such as Shanghai, Shenzhen, Sichuan, etc.
The South would likely hold an overwhelming advantage in GDP,
and... Korea... even if it had achieved unification, it would probably be much poorer than it is now..