I would add this here - Russia, having previously delivered ultimatums a couple of times, and having received what it wanted, decided that they would continue to calmly achieve their goals by the method of threats, blackmail, ultimatums, and their fifth column in the EU (Merkel, Macron and many others) . They were sure that the EU, the USA, Britain would allow Ukraine to be swallowed up, once again closing their eyes or "expressing concern."
The sad thing is, nobody could stop them and they realized this long time ago. I mean what could the world do about it? The power of nuclear they have, and the willingness to use it if they are not given what they want to creates the biggest issue right now.
What we are looking at right now is the fact that Russia could do whatever it wants, and if you do not do just sanctions, if you do something militarily, like send soldiers, then they will send nukes and that's it, there is no discussion after that and everyone is afraid of that. I do not think that Russia will stop here, they will do whatever they want to do, because nobody else could top them.