1) It's not about defending ourselves from foreign invaders, so we have no business here, regardless of whether we think slightly better about the cunts in Moscow or the cunts in Kiev;
2) You're a fucking idiot if you interpret an arms reduction agreement as promise of military aid, and so was the Ukraine;
3) The US has been in full imperialism mode since the '40s. It is never a good time to invade the US;
4) The artificial creation of the Ukraine was the first problem;
5) The undemocratic overthrow of the Ukrainian government was the straw that broke the camel's back;
6) This doesn't make Russia's behaviour correct;
7) There is no correct behaviour.
That you refer to 'the Ukraine' shows that you are neither Russian nor Ukrainian and misinformed even about the name of that country.