there are wars for all reasons - self defense from NATO encirclement and be warred agaisnt in a proxy manner is another
the only maxim i know that fits war is "War is the ultimate failure of diplomacy"
NATO is not an offensive organization. It was designed to act when Russia attacked a neighbor. However, you have to be in NATO for that to happen. Ukraine is not. Existing is not a cause of war. Putin is waging a war of choice.
Putin eschewed diplomacy and went straight to Defcon 3.
This is Putin's war. Ukraine did nothing except became capitalistic and westernized by choice. That is not a cause of war. Putin was looking for one and decided "fuck it, I will do it anyway".
