Way of life typified by the lack of permanent settlement and usually cyclical movement from place to place, which arose in the 8th century BC, and continued as an important force in world history until the 18th century AD. Hunter-gatherers are usually nomadic, but most nomads are pastoralists, moving in search of new grazing for their herds. Those who have permanent homes but leave them periodically are said to be semi-nomadic; those who move seasonally are said to practice transhumant pastoralism. Nomadism has been typical of the Eurasian steppes and of north Africa. The sudden arrival of large groups of nomads caused severe alarm to more settled societies.