What does he want from his war or does he really know anymore?
all that was part of the agreements made when the soviet union dissolved.... and many on both sides believed at the time that NATO.. which was originally created to counter soviet agression... would itself be dissolved once the soviet union became russia again and the agression ceased........Ukraine wants to join NATO, and Putin doesn't want NATO right up against Russia's border like that. He has long insisted that Ukraine maintain strict neutrality and give up on joining NATO.
He also fears Russia being encircled by democracies, which would be a refuge for dissidents and a threat to his own power. Ukraine is a foil to the Russian autocracy.
He's probably also trying to re-establish a Russian empire of some kind.
Also doesn't hurt that Ukraine has abundant natural resources, including arable land and lithium.