How does the experience of the Niger Valley challenge conventional notions of civilization?

The experience of the Niger Valley challenged conventional notions of civilization because they had an absence of a corresponding state structure. Unlike the cities of Egypt, China, and the Roman Empire, or Axum, these middle Niger urban centers were not encompassed within some larger imperial system. They also didn't have despotic power, widespread warfare, or deep social inequalities. They had a growing network of indigenous West African commerce. They were cities without states.