 Originally united with Belarus and Muscovy under the state of Kievan Rus', a schism took place after the Mongol invasion, as the Muscovite lands stayed under Mongol/Tatar rule for another century and Ruthenian (Ukrainian/Belarusian) lands were taken over by the ascendant Duchy of Lithuania, as it helped Ruthenians drive out the Mongol invaders.During this time a language separate from Old East Slavic evolved on the territory of the progenitor Russian principality Muscovy, while a Ruthenian language continued evolving on the territory of central Kievan Rus' (Ukraine and Belarus), whose people were known as the Ruthenians.While Muscovy stayed under Mongol control for over a hundred years, it absorbed much Mongol vocabulary, thus separating modern Russian from modern Belarusian and Ukrainian.