as said, they did literally that in 2014. sure, there have been some local happenings here and there, but back then ukraine didn't go into a full blown defensive war despite having large parts their territory invaded and annexed. look where it got them. why would they repeat the same mistake twice? russia never had any intentions on following up on any promises or international treaties, being stuck in 19th century mentality they'll jump on neighbouring countries as soon as they turn their back on them for a second.
Poland