The chiefs of the sahel grew rich from

selling water
trading gold
conquering groups
taxing traders

The Sahel (/səˈhɛl/) is the ecoclimatic and biogeographic zone of transition in Africa between the Sahara to the north and the Sudanian Savanna (historically known as the Sudan region) to the south. In the Sahel, abject poverty, fast population growth, climate change, recurrent food and nutrition crises, armed conflicts and violence converge dangerously. The chiefs of the Sahel grew rich from taxing traders. 

The zhou dynasty (1046-256 bce) was the longest-lasting of china's dynasties. it followed the shang dynasty (c. 1600-1046 bce) and it finished when the army of the state of qin captured the city of chengzhou in 256 bce.