sentences:  By the end of the 17th century, Ukrainian, Polish, and West European penetration had weakened the Russian cultural synthesis—at least among the elite—and had prepared the way for an even more radical transformation.Russia's eastward expansion encountered little resistance.In 1581, the Stroganov merchant family, interested in the fur trade, hired a Cossack leader, Yermak Timofeyevich, to lead an expedition into western Siberia.