The Sahel is a fragile semiarid region extending through 10 countries south of the Sahara. Wild ungulate populations migrate to make use of nutritious but very seasonal food supplies. In doing this, they maintain a higher population size than they could as sedentary populations. Similarly, migratory pastoralists have traditionally lived with their cattle in balance with the vegetation. This balance was disrupted in the 1950's and 1960's by (i) the settlement of pastoralists around wells, and (ii) the expansion of agriculture north into the pastoralists' grazing lands. Land was lost both from overgrazing and from planting with cash crops coincident with increasing human and cattle populations. This has resulted in continuous famine in various parts of the Sahel since 1968. In addition, widespread soil denudation may be causing climatic changes towards aridity. Long-term climatic trends in the past 3000 years point to human interference rather than climatic change as the cause of the famine. The evidence suggests that the Sahel problem (i) is a man-made famine caused by overgrazing and not by lack of rain, (ii) was exacerbated by piecemeal development aid projects, and (iii) has been present for two decades. Also (iv) emergency food aid by itself will aggravate the problem, so that (v) food aid can only be acceptable if tied to long-term care of the people and regeneration of the vegetation.