While the encroaching containment effect of NATO encircling Russia is certainly true, there is a key difference between "NATO expansion" and what Russia has been doing since 2014.
NATO is a voluntary organisation where new members request to join, this is why something like a Referendum was always the most peaceful option - but only if Russia could accept its result which considering what has happened is doubtful. If Russia wanted to peacefully stop the encroachment of NATO around them, they only had to treat their neighbours well.
US Imperialism is real, and fucked. That doesn't mean Russian Imperialism isn't.
Also Putin isn't reforming the Soviet Union he's re-establishing the Kievan Rus which was the time when the Rus people were the nobility above the Slav people. Genetically yes, Rus and Slav are essentially the same thing. But Historically the Rus dominated the Slav people and this where are all those great Eastern European fractures formed that continue to affect modern day borders. This is why Putin can see Ukraine as simply a belligerent Russian territory, he's trying to reestablish some very old borders.