 The Sich, with its lands, became an autonomous region under the Russian protectorate.The Don Cossack Host, which had been established by the 16th century, allied with the Tsardom of Russia.Together, they began a systematic conquest and colonization of lands to secure the borders on the Volga, the whole of Siberia (see Yermak Timofeyevich), and the Yaik (Ural) and Terek rivers.