Read this: This influx was compounded by the decline of the Western Sudanic Mali Empire in 1375 and the Songhai Empire in 1591. Additionally, as inland regions underwent desertification, inhabitants moved to the wetter coast. These new inhabitants brought skills such as cotton spinning, cloth weaving, iron smelting, rice and sorghum cultivation, and social and political institutions from the Mali and Songhai empires. Shortly after the Mane conquered the region, the Vai people of the former Mali Empire immigrated into the Grand Cape Mount region. The ethnic Kru opposed the influx of Vai, forming an alliance with the Mane to stop further influx of Vai.[citation needed]
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What happened when regions underwent desertification?
inhabitants moved to the wetter coast