Russia is aggressor and are even in these times occupying countries with clear borders and killing civilians and in the same NONE of the NATO countries are doing something even similar since WW2.
None? What about Yugoslavia, Libya, Iraq?
Clear borders? Ukraine? You have documents?
Then go to international court and present them. Prove your claims.
Specifically, prove your claim to Sevastopol, that didn't return in the 90-ies only because Russian parliament was shot at by traitor Yeltsin.
During the split of USSR:
Kravchuk: And what will we do with Crimea?
Yeltsin: Help yourself (Da zabiray!)