> assured Gorbachev on February 10, 1990: “We believe that NATO should not expand the sphere of its activity.” (See Document 9) After this meeting, Kohl could hardly contain his excitement at Gorbachev’s agreement in principle for German unification and, as part of the Helsinki formula that states choose their own alliances, so Germany could choose NATO.

So, if unified Germany could choose NATO - that will mean that NATO is expanding.

So, basically TLDR - some vague promises to Soviet Union, some vague promises from Soviet Union.

Of course current Russia will twist history the way they want.