Turkestan and then across Siberia as far as the Amur.
The decay of Mongol energy in the seventeenth and eighteenth centuries is very difficult to explain. Within two or three centuries from the days of Jengis and Timurlane Central Asia had relapsed from a period of world ascendancy to extreme political impotence. Changes of climate, unrecorded pestilences, infections of a malarial type, may have played their part in this recession—which may be only a temporary recession measured by the scale of universal history—of the Central Asian peoples. Some authorities think that the spread of Buddhist teaching from China also had a pacifying influence upon them. At any rate, by the sixteenth century the Mongol, Tartar and Turkish peoples were no longer pressing outward, but were being invaded, subjugated and pushed back both by Christian Russia in the west and by China in the east.
All through the seventeenth century the Cossacks were spreading eastward from European Russia, and settling wherever they found agricultural conditions. Cordons of forts and stations formed a moving frontier to these settlements to the south, where the Turkomans were still strong and active; to the north-east, however, Russia had no frontier until she reached right to the Pacific....