Russia never was a formal NATO member. There was a succession of mutual treaties and collaboration agreements, the last of which was the NATO-Russia Council. Russia is a permanent member of the United Nations Security Council, and as such, has veto power there; this in turn passes resolutions which provide the mandate for NATO interventions. The only organization I can think of that Russia was kicked out of following the Crimea annexation is the G8, although that’s not really something that issues a formal membership.
But it’s true, of course, that Russia and Putin specifically was at times at least quite sanguine about Ukraine’s possible NATO membership, such as the famous quote from 2002 where he essentially said that this is a question between Ukraine and NATO. Furthermore, the Baltic states, themselves former Soviet republics, joining NATO never seem to have disturbed him much, and neither has the joining of Sweden and Finland in the wake of the Russian attack on Ukraine. The latter in particular got him exactly what he’s claimed to want to prevent, namely, a larger direct border with the NATO—and it’s not exactly something that was hard to predict.
Furthermore, any possible date for Ukraine joining NATO would’ve been decades into the future, and NATO was in fact in the process of demilitarization across Europe before the attack—so not only was Putin rather inconsistent in his estimation of the ‘danger’ posed by NATO, but he seems to have reacted to it in the singular way that would guarantee it becoming much more severe.
But the case that Putin had different interests in attacking Ukraine can also be made in a more definitive way, I think (having had some cause to look into this some time back). You don’t need to engage in any complicated who promised what to whom, or who intervened in which revolution, and so on, it’s enough to just look at the data, as measured by any one of several indices that can be used as a proxy for democratic values. For instance, here’s the human rights index for Ukraine over the last 80 years or so:
The biggest jump is the dissolution of the Soviet Union. Then, in 2004, the Orange Revolution sees again a definite increase, with a large decrease coming in 2013 when Viktor Yanukovych suddenly reneges on the EU-Ukraine Association Agreement, instead accepting a Russian offer. This is then followed by the Euromaidan-protests and the Revolution of Dignity in 2014, which starts again an upswing, and prompts Russias annexation of Crimea. This briefly halts the upswing, but after it picks up again in 2019, when Zelenskyy is elected, we get the full-scale invasion of 2022. (You get pretty much the same picture choosing instead, e.g., the Freedom of Expression Index or the Freedom of Association Index.)
We get much the same picture looking at Georgia:
A steady climb following the dissolution of the Soviet Union, then a pronounced jump with the 2004 Rose Revolution, and the following dip marking the 2008 Russo-Georgian war.
It’s also interesting to look at the data for Russia itself (again you can also look at other indices):
There, too, we see a pronounced raise after the Soviet years, a short plateau, and then a continuing decline, starting in 2000—the year Putin (first) assumes the presidency.
So the first story, where Putin reacts to some NATO ‘threat’, has him be extremely inconsistent about this, while simultaneously reacting to it in the dumbest way imaginable. On the other hand, if we suppose Putin is just an authoritarian looking to suppress democratic tendencies in his sphere of influence, this seems like it accords very well with the data.
The neat thing about this, in my opinion, is that even if people claim (as they do) that the revolutions in Georgia and Ukraine are just due to Western (read: US) meddling, you can still point to the fact that they evidently succeeded in increasing individual freedom and human rights, which seems rather desirable to me; and then point to the fact that it is these heights that seem to correlate well with Russian military interventions, and nothing besides really.