The whole frontier between Europe and Russia is a mess for a long time because of the Russian and to a lesser extent, German tendency to invade and replace native people. This leads to perpetual internal strife which Russia is now exploiting by claiming that they're just looking out for poor oppressed ethnic Russians. At the end of WWII Russia cleansed eastern Europe of Germans only to replace them with Russians.
From Schindler's list. Basically 'You've been liberated, now get out'
Russian officer: You have been liberated by the Soviet army!
Itzhak Stern: Have you been in Poland?
Russian officer: I just came from Poland.
Itzhak Stern: Are there any Jews left?
Michael Lemper: Where should we go?
Russian officer: Don't go east, that's for sure. They hate you there. I wouldn't go west either, if I were you.
What Russia did...starting with Stalin...was to move ethnic Russians into thei occupied SSR's in order to spread the influence of Russian culture...history...language etc. and try to erase the original culture of the SSR's.
Putin is playing on that now saying that where ever ethnic Russians are he has the right to come in and defend and or liberate them...without mentioning they weren't originally from the areas he seeks to reclaim.
That was his excuse with Osstensia (SP)...the Crimea...where the myth that the Tartars were NAZI sympathizers permeates even today in the West with Putin defenders...and in the Ukraine.
And he's only encouraged to continue with Trump taking about waking away from NATO.