In what way was the song empire weaker than tang?

The Song Dynasty was not weaker than the Tang Dynasty. In fact, it is generally considered to have been one of the strongest and most prosperous dynasties in Chinese history. However, there were some ways in which the Song differed from the Tang:

* Military and territorial control: The Tang Dynasty had a very strong military and controlled a vast territory, including much of Central Asia. In contrast, the Song Dynasty had a smaller territory and was often faced with military threats from nomadic peoples from the north, such as the Liao and Xixia, and could only regain full control of the North when they were already declining rapidly under Jurchen attack and the Northern Song fell at last.

* Technological advancements: The Tang Dynasty saw many important technological advancements, such as the invention of gunpowder. While the Song Dynasty did continue to make some advances, overall it was not as innovative as the Tang Dynasty.