Mali lies in the semi-arid Sahel, a transitional ecozone located between the Sahara Desert and more southerly tropical savanna areas, which stretches over 3,500 km from Mauritania in the west to Sudan in the east. Years of successive drought and plagues of locusts have caused crop failure and have left vegetation stripped bare. As a result, food stores across the region are empty, herds of animals have died, and millions are hungry. Mali is one of Africa's major cotton producers. A chronic foreign trade deficit makes it nonetheless heavily dependent on foreign aid and remittances from Malians working abroad. With a magnificent history of ancient empires going back to the fourth century, Mali was conquered by the French in the middle of the 19th century. For several decades after independence from France in 1960, Mali suffered droughts, rebellions, a coup and 23 years of military dictatorship until democratic elections in 1992. Mali was regarded as a model of African democracy until the military seized power in March 2012 and the north fell under the control of al-Qaeda. Although civilian rule was reestablished in the summer of 2013, a fragile truce with Tuareg separatists broke down amid resumed fighting a year later. Poverty in Mali is pervasive. Food security is highly speculative given the harshness and unpredictability of the climate. This is compounded by seasonal variations in the weather and erratic rainfall patterns which tend to be particularly difficult to forecast during the pre-harvest period. Although poverty is predominantly a rural phenomenon in Mali, it is also a cause for concern in urban areas, where traditional networks of solidarity are breaking apart and access to food is more difficult than in rural areas. Mali's social indicators are among the worst in the world, such as low and declining primary school enrollment rate (23% overall and 17% for girls) and the low immunization rate among children (16% vaccinated against the six main childhood diseases – 30% in urban areas and 6% in rural areas). Once home to some of West Africa's most prestigious ancient universities, today, only a small minority of Malians are literate (World Bank). The country’s high fertility rates and exploding population threaten to further tax the Sahel’s limited ecological carrying capacity and provoke future humanitarian crises.