Hi mate. In this case I do absolutely believe Putin's invasion...

Hi mate. In this case I do absolutely believe Putin's invasion was absolutely inevitable as a consequence of his reaction to what would be perceived as a very perilous strategic threat to Russia. I don't say it is the right thing to do but that it was an pretty obvious self fulfilling prophesy.
If you want to see how countries react to definite threats to their territory then I suggest you look at how the Americans reacted to Soviet missiles in the Cuban missile crisis. In broad terms I can't see that much difference between the situations.