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.
You understand what the problem is with Russia's nuclear weapons - yes they do exist, yes they are ready, at least according to statements, to use them. But let's look at this situation, in a timeline of +50 years, for example. The EU and the US, for example, will surrender Ukraine tomorrow. AND ? What's next ? Is it all over? Not ! On the contrary - having felt the taste of "victory" Russia will say - now hand over the Baltic countries to me! And what to do again?
I will now give a very simple example, but very clear. "Russian World" or rashism is an oncological disease that is now trying to hit the world. If you have come across this class of diseases, then you know how it is treated - very painful and destructive procedures of chemotherapy or radiotherapy. This creates a terrible side effect. BUT ! The only way to cure cancer is to KILL IT! The situation with rashism and its nuclear weapons looks exactly the same. You can not give in and give up, only win! Only destroy otherwise he will destroy all of us, someone before someone a little later ...