Also it's fundamental for the fiction of Russia as the successor state of the Kievan Rus¹ to hold Ukraine, instead of client state of mongols.
I suppose this leads to need to be part of "Europe".
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¹ it is not unheard that empires use names and/or creative interpretation of history as justification of destiny.²
² The USA13 expanding west while breaking countless treaties and practicing genocide under idea that they were "America" and Americans were "Indians".