place either in or near these two passages. It would seem in fact as if from the earliest times action and reaction, movements and counter-movements, have been going on between the peoples of Europe and Asia. What has caused this continuous unrest? One may attribute it perhaps to religious impulses, like that which inspired the Arabs, or to abstract ideas, which aimed at giving to mankind a uniform political and legal system, such as those which moved the Romans. This explanation will only suffice if we assume that the impulses which lead man to change his modes of thought and his habits of life, come direct from the "free spirit", untrammelled by the chains of material existence. If that is so, then these spiritual movements cannot be traced to peculiarities of climate or geography. But if on the other hand they are connected with the material side of life, then the structure of continents, their temperature, soil and climates, must influence the human types that live there, and must affect the forms of society and the different political and religious movements that take place there.
Now Central Asia is a huge expanse of alternating high plateau and low plain, divided by great ranges of mountains. The climate of one part of it is widely different from that of another. Physical obstacles have prevented the people of Asia from uniting in one common political system. The history of Central Asia from the Islamic renaissance to the Mongol Empire may be regarded as an attempt to create this unity. But the caprices of nature have always frustrated the ideals of man. The rulers of the Bactrian oases could subject their own neighbours, but they could not make their influence felt beyond the Pamirs or the Tian-shan. The Bedouin
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