> The US secretary of state, James Baker, promised Russia that NATO would not expand eastward if Russia withdrew its military from the Warsaw Pact countries

No, he didn't.

And even if he did promise the USSR that, I don't see a signed international agreement. Any such personal assurance with no formal agreement could not reasonably be viewed by anyone as anything more than a statement of policy of the then-current administration, not an open-ended binding commitment. I do see a signed treaty, signed much later, committing Russia to respect the sovereignty and territorial integrity of Ukraine, that was in force when it invaded and occupied much of Ukraine.

Except he didn't promise the USSR anything like that. The only commitment he made was to relay the request for a commitment to not expand NATO to the US negotiating team. It was rejected by the US team and the language the USSR suggested never made it into any treaty.

I think that's fair, but it's not like the former communist countries were forced at gunpoint to join NATO.

Russia may not like it (and I'd imagine I wouldn't were I in the same position) but invading countries because of their own sovereign decisions is unlikely to be successful in the long-term.