sentences:  Yermak defeated the Khanate of Sibir and claimed the territories west of the Ob and Irtysh Rivers for Russia.From such bases as Mangazeya, merchants, traders, and explorers pushed eastward from the Ob River to the Yenisei River, then on to the Lena River and the coast of the Pacific Ocean.In 1648, Cossack Semyon Dezhnyov opened the passage between America and Asia.