> IMO its the same as the Russia – Ukraine – Belarus thing.

What is the same thing about Ukraine, Russia, Belarus today? Different Slavic and non-Slavic tribes participated in ethnogenesis of Belarusians, Ukrainian, Russians.

Belarusians : Dregoviches, Radimiches, Polochans, Balts
Ukrainians: Drevlyans, Uliches, Tivercy, Polians, White Croats, Drevlians, Severians, possibly Sarmatians
Russians: Viatyches, Novgorodian Slovenes, Kriviches, Severians, Finno-Ugric

Ancestors of Russians, Belarusians, Ukrainians were in the same ancient Rus state for around 200 years. By the time Rus disintegrated after Yaroslav the Wise around 1050 people of Rus identified themselves by tribal names as per monk Nestor who compile the Tale of Byone Years. Later, these people lived in separate states – the Grand Duchy of Lithuania/Polish-Lithuanian Commonwealth & Muscovy Principality/Russia till 1795.