Why was Zhao Kuan-yin unable to unite all of China in the 10th century, and Yang Jian in 589 was able to do this?

In the Yang Jian era, the state structure of neighboring nomads was still primitive, they failed to organize the lands they conquered in China and lost the competition with the Sui empire.In the 10th century, the Khitan adopted Chinese culture so much that they managed to provide their subjects in North China with a life no worse than it was southerners in the Song Empire.

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.