Man-made deserts

The history of civilizations is a record of struggles against the progressive dessication of civilized lands. The more ancient the civilization, the drier and more wasted, usually, is the supporting country. Two major factors are believed to account for the growth of man-made deserts. In the first place, semi-arid to semi-humid regions proved the most favorable sites for the early development of human culture. In the second place, processes of soil erosion are accelerated by the exposure of soil surfaces hitherto protected by complete mantles of vegetation, whether grass or forest, by heavy grazing and cultivation.