If you reversed the roles with a purely hypothetical scenario, with perhaps the U.S. & Mexico, you might just answer your own question, using your own rational thoughts.
If Mexico partnered with a committed & admitted Nazi group, for example, to gang up on American ex-pats living in Mexico yet were loyal to the U.S. These ex-pats were being constantly under attack, given formal recognition and acceptance by Mexico to these Nazis, to run rough shod over Americans living in Mexico.
Would you say that the U.S. would be justified in leading an armed invasion force into Mexico to stop the violence being committed upon these ex-pats?
That scenario is exactly what has been occurring in Eastern Ukraine for the past eight years.
“... to gang up on American ex-pats living in Mexico yet were loyal to the U.S. These ex-pats were being constantly under attack, given formal recognition and acceptance by Mexico to these Nazis, to run rough shod over Americans living in Mexico.”
If that hypothetical scenario were real, the ex-pats would just leave Mexico and return to the US. Rather quickly I imagine.
Which is why nobody really believes Russia’s flimsy excuses that they need to invade Ukraine (or Crimea, or Moldova, or Georgia, etc, etc) to protect Russians. They could just offer these Russians refuge right across the border, but they don’t, because then they would lose their excuse to invade and conquer territory.