The Russian conquest of Siberia took place in the 16th, 17th, and 18th centuries, when the Khanate of Sibir became 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. It is traditionally considered that Yermak Timofeyevich's campaign against the Siberian Khanate began in 1581. The annexation of Siberia and the Far East to Russia was resisted by local residents and took place against the backdrop of fierce battles between the indigenous peoples and the Russian Cossacks, who often committed atrocities towards the indigenous peoples.