What internal political problems of the Tang Empire stemmed from its “multinationality”?

What internal political problems of the Tang Empire stemmed from its “multinationality”? Did the Tang rulers manage to solve these problems?

The internal political problems of the Tang empire were reduced to interethnic conflicts within the ruling class (for example, court eunuchs against the governor-border guards). For three centuries, the Tang emperors usually succeeded in stifling these conflicts without leading to a civil war.

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