I was just looking at a map of the Russian ethnic majorities. Actually, they are the far eastern provinces, but also those immediately north of Crimea and over to Moldova.
I understand there are Russian troops in Moldova, but I cannot recall where I heard that...so I could be wrong.
If I were Putin I would cut off the Black sea and land lock Ukraine. Then the oil and gas pipelines from the Middle east would be controlled by Russia.
That would pretty much put Ukraine back to third world status at the whim of the Russians.
Transnistria - a breakaway region in Moldova, supported by Russian military.