ROM ancient times the most accepted writers have considered the life F of the steppe nomads of the old world to be as changeless as it is barbarous. This may be described as the classical view. It has been elaborated, without being really changed, by those geographical determinists who believe that primitive human society is controlled rigidly by its environment. Proceeding from this assumption, they describe both the occasional overrunning of settled lands by nomads and the occasional advance of settlers into nomad territory as "waves," which are caused by variation, notably climatic variation, in the geographical environment. More recently, this classical view and its geographical explanation have been modified by writers who believe that human society is capable of modifying its geographical environment. Both the cultivation of marginal areas and the overgrazing of stock in true steppe areas can ruin the soil, create deserts and "change the climate.', This may be called a semi-classical view. My own opinion is that the relation of history to geography is much more complicated; that steppe society has been modified by both evolution and devolution, and also by shifts between extremely extensive forms of economy and relatively intensive forms. I believe that while the environment strongly conditions a primitive society, it does not always make social evolution impossible. Moreover society, as it evolves, attempts to exercise choice and initiative in the use of the environment. Consequently, marginal environments and marginal societies, permitting initiative of this kind, are of special importance in studying the way in which historical movements are generated. In attempting to establish this opinion, I shall first review the classical concepts and their modern variants, and in so doing set out the grounds which, I think, justify my own concept. In his encyclopaedic 'Study of history' Mr. Arnold Toynbee made a notable attempt to survey all the geographical factors in the history of nomadic peoples in the whole steppe zone of the old world, from North Africa across