Answer:
the climate became warmer and the desert expanded
Explanation:
The Sahel region is the region of ecoclimatic as well as biogeographic zone of the transition in the Africa between the Sudanian savanna to the south and Sahara to the north.
At around 2000 BCE, the agricultural techniques of the people of the Sahel region started spreading or diffusing to the other parts of the Africa due to the climate change. The climate became more arid and warmer gradually and the deserts also expanded in the region.
