(1) There have always been those in high power who sought to restore the old U.S.S.R., Putin is the fall guy for them.
(2) Putin and his cronies know they will never get Ukraine back the way they anticipated. Knowing this are set on a scorched earth policy destroying everything possible. Killing Ukrainians either directly or by destruction of their infrastructure and through starving them to death. Call it what it is, ethnic cleansing.
No matter how this ends it will be miserable for the Ukrainians who most likely won't see the country back the way it was for many, many years. Perhaps a century or more.
It's been said by critics the reason Western nations are making a fuss is these people are almost entirely white Christians. Are we to feel guilty about that? I certainly don't think we should. What's wrong with being a white Christian?