It’s safe to say Ukraine is an existential threat to Putin. Russia as a nation shouldn’t care that Ukraine is democratic and integrating with Europe, except to ask why they couldn’t also.
The NATO-US acting from Ukraine possibly attempting to foment "color" revolutions in Russia, NATO missiles on Ukraine soil, an increasingly belligerent leader in Ukraine renewing the push to join NATO and NATO-US arming and training Ukraine troops. These seem to be more likely factors in the invasion.
Given that the "West" has been frothing around the mouth for his ouster (he did once ask to join NATO btw), one could conclude that "He who goes first wins" was a viable strategy for him.