During the epic drought of the 1970s and 1980s, 30 percent less rain fell in the Sahel compared to the 1950s and more than 100,000 people died. Basically it was the biggest drought over the largest land area of the 20th century, according to the Geophysical Fluid Dynamics Lab at Princeton (GFDL).
At that time most believed the cause of drought was human overuse of the land—grazing, deforestation, poor farming practices—on a local scale. Nowadays the data suggest recurring Sahelian droughts are driven by a more complex constellation of factors, some related to global climate change, including:
Warming sea surface temperatures in the Indian Ocean (see this paper in Science)
Increase in greenhouse gases combined with increase in atmospheric aerosols (see GFDL)
Changes in the Atlantic multidecadal oscillation, which may or may not be manmade (see this paper in International Journal of Climatology)
Sadly 2012 has produced another drought in the Sahel, only two years after the 2010 drought. Water shortages, failed crops, insect plagues, high food prices, human displacement, conflict, and chronic poverty now threaten the lives of 18 million people in the region, including at least a million children, says UNICEF.