There is no way once a country has nuclear weapons to deter them without risking nuclear war. This does not mean appeasing them and giving them what they want is the answer. There is risk in life.

Russia was appeased long before this. Everything they took and did that was atrocious was met with very little resistance from the west. It started to look like Hitler 2.0. Putin was just going to keep going bigger and bigger until he got a response. Trying to take all of a country was a step too far.

But, if Europe had accepted his taking of Ukraine without sanctions or supplying weapons meaning an easier victory over Ukraine, then Finland, etc. were next. He had to be stopped somewhere. I guess unless your one who believes nuclear war should be avoided at all costs to the point of him being allowed to take all of Eastern Europe to redo the USSR of old. Even then he's a mad man, so he could press the buttons at any time. Not sure what kind of checks and balances they have there for use, but I would guess it is not much.