Geographical Motivations for Change. From the sixth through the sixteenth centuries, five major factors motivated change in the Western Sudan: expansion of reliable food production, the establishment and stabilization of governments, the creation of control over intra- and interregional trade routes and shifts in who exerted such power, war and resulting migrations, and natural and man-made catastrophes. (Though they were manifested in different regional circumstances, these same five impetuses drove the evolution of Asian, European, Mesoamerican, and Near Eastern societies.) During the 500-1590 period, there developed a series of Sudanic-Sahel regional civilizations that were able to produce surpluses of foods such as millet, sorghum, rice, and other crops in the desert fringes, the savanna grasslands, the edges of the forest areas, and the basins of the Senegal and Niger Rivers and Lake Chad. These civilizations successfully adapted to regional soil conditions...