Ukraine is all about a warmwater port for Russia, and the territory needed to use it.
Remember when the world was worried about Soviet Nukes in Ukraine. I’d forgotten too until being reminded. The UK, US, and Russia promised to defend Ukraine boarders forever if allowed to go into the country and dismantle and remove them. Turns out it was never an actual treaty binding on anyone.
Opps!
Best case, the eastern quarter of Ukraine is deeded to Russia, Ukraine keeps the rest, expands their port at Odesa, and immediately joins NATO to prevent further loss. Which is why Russia is already raising a stink over NATO expansion now.
Of course, that's not how it's shaping up now.