Politicians face three major problems with big decisions like war:
1. What should I do?
2. How do I sell it to the people at home?
3. How do I sell it to the rest of the world?
I think that accounts for why some correctly observe Putin claimed Ukraine needed to be "liberated" from all the Nazis (#2 above). It's also why Russia has said repeatedly that NATO caused the war (#3 above).
As for the actual cause (#1 above), like all wars, there are probably multiple factors, like:
1. Former KGB Putin and plenty of others longing for the "glory days" of the USSR.
2. A desire to stop NATO expansion by intimidating anyone else who might want in.
3. Removing the Zolynksy government and replacing with a pro-Russia government.
4. Solidifying access to the Black Sea and claims to Crimea.
...
ETA: also remember, if news reports are accurate, Putin thought this war would be a 5-minute cakewalk. I suspect Russia might not have invaded if they knew the cost in lives and dollars this war would bring.
Because Russia can't wage a par purely based on what's in Putin's head. The assumptions and beliefs of any given leader ends up encoded in both internal policy memos, and in the observed strategic decisions made by the various agencies tasked with executing on said leader's goals. Both are places where external observers can infer what is going on in the upper levels of the government.
1. What should I do?
2. How do I sell it to the people at home?
3. How do I sell it to the rest of the world?
I think that accounts for why some correctly observe Putin claimed Ukraine needed to be "liberated" from all the Nazis (#2 above). It's also why Russia has said repeatedly that NATO caused the war (#3 above).
As for the actual cause (#1 above), like all wars, there are probably multiple factors, like:
1. Former KGB Putin and plenty of others longing for the "glory days" of the USSR.
2. A desire to stop NATO expansion by intimidating anyone else who might want in.
3. Removing the Zolynksy government and replacing with a pro-Russia government.
4. Solidifying access to the Black Sea and claims to Crimea.
...
ETA: also remember, if news reports are accurate, Putin thought this war would be a 5-minute cakewalk. I suspect Russia might not have invaded if they knew the cost in lives and dollars this war would bring.