Desert Frontier is a study of the ecological and economic impact of a long-term trend toward increasing aridity along the southern edge of the western Sahara. Beginning in the early seventeenth century, this climatological trend forced the desert approximately 200–300 kilometers to the south, transforming ethnic identities and ways of life along the length of the Sahel. Based on extensive archival research and on Saharan oral data, Desert Frontier argues that the principal historical dynamics of the precolonial Sahel were determined by this pervasive ecological crisis, rather than by the dynamics of a European-dominated world system.