Deserts are formed by natural processes interacting over long intervals of time. Paleodeserts, large sand seas, now inactive because they are stabilized by vegetation, extend well beyond the present margins of core deserts, such as the Sahara desert in Africa.
Desertification is a complex process, involving multiple causes and proceedings at varying rates in differing climates. It may intensify a general climatic trend towards greater aridity, or it may initiate a change in local climate. Areas far from natural deserts can degrade quickly to barren soil, rock or sand through poor land management.
Desertification became well known in the 1930's, when parts of Great Plains in the United States turned into the "Dust Bowl" as a result of drought and poor practices of farming, although the term itself was not used until almost 1950. During the dust bowl period, millions of people were forced to abandon their farms and livelihoods. Greatly improved methods of agriculture and land and water management techniques in the Great Plains have prevented that disaster from recurring. But desertification presently affects millions of people in almost every continent.