The cultural divide across the Dneiper is very bitter and deep, Europe (especially Eastern Europe, which I class as a separate subunit inside Europe) gets the more productive part and cuts away the less productive part to Russia. The prosperous Western Ukraine (or whatever name they come up with. Any Eastern European/Russian history buffs out there?) will help anchor and stabilize Eastern Europe and shield the Balkans and "Latin" Europe from Russia as well.
No buff me but interested amateur....
IMO the key elements of interest are two separate peoples: The Rus and the Khazars.
The Khazars are/were descendants of Attila's Huns, the Avars and the Gokturks. They dominated the Silk Road from the Dniepr to the Altai (and apparently had a Jewish connection - as well as just about every other religion).
The Rus are usually considered by Westerners to be Vikings and by the Russians to be indigenous Slavs. IMO - probably a bit of both.
630 AD - Constantinople starts treating the Khazars as a fellow state with Anti-Arab interests.
750 AD - Vikings settling on Lake Ladoga
775 AD - Khazars marry into the Byzantine royal family and Leo the Khazar is emperor of Byzantium - causes a ruckus with Rome because he doesn't like graven images.
859 AD - Rus or Vikings at a York Factory type trading post at Novgorod
882 AD - Rus seize the Kiev trading post from the Khazars
969 AD - Rus seize the Khazar capital of Atil on the Volga delta draining into the Caspian sea - Khazars lose control of the Silk Road
1147 AD - Rus have established a trading post among the Slavs at Moscow
1223 to 1240 AD - Mongol conquest of the Rus
Mongols' Golden Horde holds the Silk Road until bypassed by Vasco da Gama and later the Dutch East India Company.
I leave it others to figure out who holds title to which lands under what names. (I haven't touched the Bulgar claims to the lands).