Rus'

More precisely - Kievan Rus'

Kievan Rus' was a loose federation in Eastern Europe and Northern Europe from the late 9th to the mid-13th century. Encompassing a variety of peoples, including East Slavic, Norse, Baltic, and Finnic. It was ruled by the Rurik dynasty. The modern nations of Belarus, Russia, and Ukraine all claim Kievan Rus' as their cultural ancestors, with Belarus and Russia deriving their names from it. At its greatest extent in the mid-11th century, Kievan Rus' stretched from the White Sea in the north to the Black Sea in the south and from the headwaters of the Vistula in the west to the Taman Peninsula in the east, uniting many East Slavic tribes.