Before revision: The Sahelian kingdoms were a series of centralized kingdoms or empires that were centered on the Sahel, the area of grasslands south of the Sahara, from the 8th century to the 19th.
After revision: The Sahelian kingdoms were a series of centralized kingdoms or empires that were centered on the Sahel, the area of grasslands south of the Sahara, from the 1st century to the 19th.