Russia has fought different wars for different reasons
NATO expansion doesn't explain all of Russia's aggression, but it surely explains some of it.
People who don’t know the history are easily susceptible to propaganda. They will believe that Russia attacked Ukraine because of “NATO’s expansion” or the Revolution of Dignity. Remember the "special military operations" in Transnistria, part of Moldova in 1992, and Abkhazia and South Ossetia, parts of Georgia, in 1993, then again Georgia in 2008, then Crimea in 2014. So it was never about the "NATO expansion" such as some paid propagandists and gullible Westerners blabber about, but about reconstituting the Russian Empire, since practically the day its latest iteration, the Soviet Union, fell.
If simplification is the surest sign of propaganda, then what can we call this? It is one thing to say that Russia only went to war because of NATO, which has indeed been the line of some dopey heterodox anti-imperialists for quite some time. But it is not much different to say that Russia only went to war because of its imperial ambitions — and it is even more simplistic to pretend that the inherent aggression of the Russian Soul or whatever explains the conflicts in Transnistria, Abkhazia, South Ossetia, Georgia, and Ukraine.
Lumping the Transnistria War in with the war against Ukraine, for one, is particularly daft. They are comparable in the sense that both were wars that pit locals who still valued their Soviet / Post-Soviet identity against nationalists who wanted a decisive break from it, but that is about as far as it goes. One major difference, for example, is that it was the nationalists who were breaking from a long-established status quo in the early 90s, whereas it is the separatists allied with Russia who were breaking from a long-established status in 2014. Another curiosity here is that Ukrainians mostly allied with rogue Russians in support of Transnistria during their war — in fact, one faction of Ukraine’s hard right hoped to annex it. There is also, of course, the detail that Russia was officially neutral in Transnistria, and its behavior is ultimately hard to square with a plausible theory of imperial ambition.
In Ukraine, NATO and Russian expansionism were both clearly factors, but even if we account for both of them we are missing major pieces of the runup to war. The political struggle between the EU and Russia’s Customs Union for trade deals with Ukraine, for example, can neither be reduced to military or territorial expansion concerns; this was a classic conflict of economic imperialisms in the Leninist sense. The Maidan revolution can’t be explained outside of that context, and even if you exclusively subscribe to an expansionist theory of Russian aggression it is bizarre to ignore the role that conflict played. Would Putin have had a pretext to invade Crimea without it? Hard to say.
Regardless, it seems silly to pretend that a land bridge to Crimea would not be an immensely valuable prize for Putin, and that he would not take it if he could get it, and that it is just a happy coincidence for him that the provinces his military has managed to capture are the exact ones that give him that bridge. On the other hand, it also seems bizarre to imagine that Putin did not regard Ukraine membership in NATO as threatening; indeed, even the most rabid online hawks rarely pretend otherwise.1 One does not have to relieve Russia of its ultimate responsibility to stay on its own side of the fucking border to appreciate how NATO expansion made it less likely that it would.
The usual line, recall, is not that Putin was unafraid of NATO — it’s that he shouldn’t be, since it is supposedly just a defensive alliance and no threat to a peaceful Russia. Evidently Roman has noticed the problem with this reasoning: even if NATO is a purely defensive alliance (lol), it does not follow that folding in new members at the border is a wise defensive move for the US or Ukraine. If dangling membership in front of Kyiv guarantees war with Russia, while abstaining to do so makes it a mere possibility, which bet is the safest?