 Complete the following phrase:  By the beginning of the Age of Discovery, many of the former principalities of Kievan Rus were integrated by the Grand Duchy of Moscow. Proclaimed the Tsardom of Russia, by the end of the 16th century the state had colonized the easternmost territories of Europe by conquering the Khanate of Kazan in 1552 and the Khanate of Astrakhan in 1556, thus gaining full control of the Volga River valley. The road to Asia was opened, and in 1581 Yermak Timofeyevich crossed the Ural Mountains with a band of adventurers, defeated the Siberian Khanate and started the 