The Russian conquest of Siberia took place in the 16th and 17th centuries, when the Khanate of Sibir had become a loose political structure of vassalages that were being undermined by the activities of Russian explorers. Although outnumbered, the Russians pressured the various family-based tribes into changing their loyalties and establishing distant forts from which they conducted raids. To counter this, Kuchum Khan attempted to centralize his rule by imposing Islam on his subjects and reforming his tax-collecting apparatus.