The resettlement of peoples in the IV-VI centuries “mixed” the Chinese with their neighbors in a way that had never happened before. As a result, the imperial army (of the barbarians) and the agricultural population of China were, as it were, two different peoples living separately. As long as this division persisted, the Tang Empire flourished.
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.