It can certainly be argued that NATO expansion was bad policy, intrinsically antagonistic, and basically in the wrong spirit of the way the world should have re

It can certainly be argued that NATO expansion was bad policy, intrinsically antagonistic, and basically in the wrong spirit of the way the world should have re-organized itself post-1989. That's actually my gut feeling as well. But it doesn't rise to level of casus belli or even a rational reason for Russia to feel directly (tangibly) threatened. And it's definitely not the "reason" Putin started the war. And you're leaving out other stuff, such as the fact that Yeltsin greenlighted the earliest round of new admissions (PL, CZ, HU), and that Gorbachev himself downplayed the significance of the expansion issue during negotiations to which you are referring -- as he made clear in that famous RBTH interview: "The topic of 'NATO expansion' was not discussed at all, and it wasn't brought up in those years. I say this with full responsibility. Not a single Eastern European country raised the issue, not even after the Warsaw Pact ceased to exist in 1991. Western leaders didn't bring it up either." And that while it was a constant source of tension and grumbling -- the NATO issue never seemed to matter all that much to Russia until the Rose and Orange revolutions in 2003/2004. That's what really started to make Putin's back arch -- not any paramount concerns about NATO expansion itself. As far as "antagonistic" is concerned, I think there's a much stronger case to be made in regard to the intentional decision by US policy makers not to provide extensive economic aid (a "Marshall Plan") to its former adversary, its insistence on shock reforms, and so on. But this is another topic. And it's not as if Russia didn' also "behave in an antagonistic/untrustworthy/threatening manner" against its would-be benefactor during its hour of need.[0][1] [0] - https://en.wikipedia.org/wiki/Aldrich_Ames https://en.wikipedia.org/wiki/Aldrich_Ames [1] - https://en.wikipedia.org/wiki/Robert_Hanssen https://en.wikipedia.org/wiki/Robert_Hanssen