This situation had first arisen, and at a very early stage, in the trans-Saharan trade. Labour was needed to work the Saharan salt deposits, and the civilizations of the Mediterranean and Middle East had long had a demand for slaves. Some North African and Middle Eastern exports, particularly perhaps horses, were so valuable in the Sudan that its kings were quite ready to exchange some of their scarce human power to secure these. However, the problems involved in marching slaves across the Sahara with its scarce and widely separated resources of water were formidable. Although reliable estimates are lacking, it ...(100 of 31209 words)