Putin has openly stated that he can never accept independent Ukrainian national identity. To Putin Ukraine is Russia. He stole Crimea in 2014 and fomented regional struggles in the east. NATO is a DEFENSIVE force. It has never threatened the sovereign borders of Russia. The more recent Russian invasion of Ukraine which continues to have genocidal intentions was a war of choice by Putin. He foolishly didn't understand the resolve of the Ukrainian people, their desire to be independent of Russia, the strength if their distinct national identity, and he predicted NATO including the U.S. would easily cave (as they did regarding Crimea). He made a big mistake. Ironically probably the biggest contributor to the strength of Ukrainian national identity and the expansion and strengthening of NATO is Putin himself! Some people like Trump call him brilliant. Not so much. His actions result in the exact opposite of what he wants.