Putin considers Ukrainians practically Russian. Cut from the same cloth. So, if Ukraine were allowed to prosper under Democratic govenment, it's a real problem for him.

He has spent decades spreading propaganda throughout Russia that the West is actually a misarable place, actually less "free" than Russia in absolute terms, and that he's providing Russia the best that is possible for Russians, and that there's something fundamentally different about being Russian that means means democracy could never work.

A free and prospering Ukraine throws a wrench in all that. If people who are practically Russian are experiancing the benefits of western democracy and they actually like it--if Russians can visit family there and experiance it themselves, then why the hell do they tolerate getting the scraps from Putin and his oligarchs? It'll all crash down.

So, his inital goal might be to take Crimea and laugh and show Ukraine is weak. He might even invaded and install his own puppet government. But creating absolute chaos and misery in Ukraine is good enough, too.

Building back a stronger Ukraine is of utmost impotance, not just for Ukraine, but for your average Russians, too.