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In page Ivan the Terrible:

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During Ivan's reign, Russia started a large-scale exploration and colonization of Siberia. In 1555, shortly after the conquest of Kazan, the Siberian khan Yadegar and the Nogai Horde, under Khan Ismail, pledged their allegiance to Ivan in the hope that he would help them against their opponents. However, Yadegar failed to gather the full sum of tribute that he proposed to the tsar and so Ivan did nothing to save his inefficient vassal. In 1563, Yadegar was overthrown and killed by Khan Kuchum, who denied any tribute to Moscow.[citation needed]