Why has China been fragmented for a long time?

First, it was poorly developed, economically, technically, politically
Secondly, because of its weakness, Western countries simply divided it into spheres of influence.
Third, the opium wars.
Fourth, a nationalist sign, the Manchus stood out in comparison with other Chinese, there was a different attitude towards them.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.