"Prior to the emergence of Kievan Rus' in the 9th century, most of the area north of the Black Sea was primarily populated by eastern Slavic tribes."
Likewise Lithuania was a union of Baltic tribes.
Later Lithuania grabbed the territory of Kievan Rus' when it was greatly weakened by the Mongol invasion.[0]
"The grand duchy expanded to include large portions of the former Kievan Rus' and other neighbouring states, including what is now Belarus, Lithuania, most of Ukraine as well as parts of Latvia, Moldova, Poland and Russia."
