"Drought is the great enemy of human civilization. Drought deprives us of the two things necessary to sustain life--food and water. When the rains stop and the soil dries up, cities die and civilizations collapse, as people abandon lands no longer able to supply them with the food and water they need to live. While the fall of a great empire is usually due to a complex set of causes, drought has often been identified as the primary culprit or a significant contributing factor in a surprising number of such collapses. Drought experts Justin Sheffield and Eric Wood of Princeton, in their 2011 book, Drought, identify more than ten civilizations, cultures and nations that probably collapsed, in part, because of drought. " Source: Weather Underground (2016).