Trade and improved agricultural techniques supports more sophisticated societies, leading to the early civilizations of Sao in the Cameroon region and Kanem in the Sahel.
“The longer you can look back, the farther you can look forward...This is not a philosophical or political argument—any oculist will tell you this is true. The wider the span, the longer the continuity, the greater is the sense of duty in individual men and women, each contributing their brief life's work to the preservation..."