The war won't have happened if the US and some western countries have kept to their promise of not expanding NATO towards Russian borders. And moreover, both Ukraine and Russia are brothers, just in arms. Russia is simply trying to survive hostile NATO policies.
Poor Putin being bullied by evil NATO... except instead of standing up to the bully he's trying to beat up his "brother". Russian family values.
To be fair, NATO was formed to secure peace in Europe, countering the threat posed at the time by the Soviet Union. Why would such pact continue not only to exist, but to evolve AND spread eastward to Russia's borders past the Soviet Union collapse?
Because Russia is still a threat as proven comprehensively by this invasion and all the other shit it's done since the collapse of the USSR.
Can you comprehend why Russia doesn't like that?
Because it has a demented wannabe-dictator who wants to rebuild the Soviet empire and NATO is kinda in the way.