NATO promised Russia it would not expand to the East.
Russia has interest in stability between Lisbon and Vladivostok – not in wars. But Russia does not accept that NATO is expanding further and further eastwards. If one speaks of provocation and escalation dominance, it is NATO that is expanding eastwards, contrary to what was promised in 1990.
Recurring pro-Kremlin disinformation that NATO had promised the Alliance would not expand to the East and that NATO is de facto aggressive.
NATO allies take decisions by consensus and these are recorded. There is no record of any decision been taken by NATO about putting a halt to enlargement to the East. Personal assurances from individual leaders cannot replace Alliance consensus and do not constitute formal NATO agreements. Moreover, at the time of the alleged promise, the Warsaw Pact still existed, which by definition could not mean joining NATO by them. Its members did not agree on its dissolution until 1991. This was confirmed by Mikhail Gorbachev himself in an interview with Russia Beyond the Headlines:
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.
Furthermore, the claim about NATO "expansion" misrepresents the process of NATO enlargement. NATO does not "expand" but considers the applications of candidate countries which want to join.
See more disinformation cases on NATO.