Fear of NATO expansion seems to be the main reason behind it. From Putins point of view, that seems understandable. What isnt understandable is why there is a need to drop bombs on apartment buildings.
There has been, and will continue to be a brain drain from Russia, and now , because of Russias actions, if they take over Ukraine, anyone with a brain will already be on their way to a safer European country which will benefit from Russias loss.
Could it escalate? A result of strangling Russias economy could be retaliation against the west, or Russia might accidently drop a bomb on a NATO country. At the moment the west seems the safest way to deal with it is to allow it to run its course as long as it is contained.