It's a testament to the awesome power of US propaganda that you can't throw a stone in Texas without hitting a house flying the Ukrainian flag, but almost no one actually knows the history and circumstances leading up to the war.
I think these two pieces provide some good background:
https://www.commondreams.org/opinion/the-war-in-ukraine-was-...
As for NATO expanding east, Russia has something of a grievance there but the U.S. and NATO should never have relegated some of the former Soviet states to the status of "buffer regions" in perpetuity in the first place. Those countries have the right to self-determination and security just like anyone else.
Well there was a bit more going on than that (for example, as to why the other members were not present, and how that came to pass).
But either way - the "coup" allegation is bogus, and not taken seriously by anyone in Ukraine.
The threat to his regime and its legitimacy is to have a democratic neighbor with russian speakers who live better lives, in what is a former colonial subject of the glorious russian empires.
NATO does make a great bogeyman though for internal audiences, to shift attention away from the futures they are deprived of by dictatorship.