Why did the rulers of the Han Empire manage to unify the culture of their subjects within the then borders of the empire

Why did the rulers of the Han Empire manage to unify the culture of their subjects within the then borders of the empire, while the rulers of the Tang Dynasty were unable to do this within the broader framework of their dominions? Can you notice anything similar in the activities of the rulers of Rome and Byzantine?

Within the Han, there was the same farming system – as in the whole of Southern Europe. Therefore, one can compare the successes of Rome and Han in the “enlightenment” of barbaric farmers (Gauls and Germans, Shu and Yue). But it was difficult for the imperial culture to penetrate beyond the boundaries of irrigated agriculture, whether it was in the mountains of Switzerland or Tibet, in the steppes of the Black Sea region or Mongolia.

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