Russia wants one small region that they lost custody of in their divorce.
This is how Czechoslovakia lost the Sudety region just before WW2. Germany also claimed that the German populace there is being mistreated and there is so much Germans living there that it should belong to Germany anyway.
Maybe this sounds a bit more familiar? Back then the West let them have it to maintain peace - funny how Russia and pro-Russians are calling for the same thing now...