In its western borderlands, Russia had come to acquire a large population of Orthodox Christians who were non-Russian. The ever-growing number of Russia's subjects now included non-Christians in the east and non-Russians in the west. Russia's steppe frontier remained ambiguous and ill defined. By the beginning of the seventeenth century, Moscow was well established in western Siberia and reached the banks of the Enisei River. Throughout the seventeenth century Russia could boast of no visible territorial expansion in the North Caucasus. Russia's advance here had been stalled for the same reasons as its march eastward into south-eastern Siberia was halted in the 1650s. In the second half of the seventeenth century, Moscow's newly claimed subjects in the west came from eastern Ukraine. The Russian conquest and colonisation policies of the mid-Volga region triggered a large-scale migration of the non-Christians. Russia's methods of conquest and colonisation appear to have formed a clear pattern.