Pastoral people in arid and semi-arid lands have, with time, developed rational sustainable land use systems based on the mobility of their livestock herds, and making optimal use of the land both geographically and ecologically. Historically such systems were self-regulating with periodic famines and disease outbreaks acting as controls. These self-regulating mechanisms are for various reasons, no longer allowed full play with resulting deterioration in land-use patterns, particularly in the settlement zones.