Russia recognised the ukrainian borders in 1994 in exchange for them giving up their nukes.
It's hotly debated but alleged that the US gave verbal assurances NATO wouldn't expand east in discussions about German reunification.
[1]: https://en.wikipedia.org/wiki/Enlargement_of_NATO#Adriatic_C...
It sure looks like it's more a fault of Russia than NATO.
Russia recognised the ukrainian borders in 1994 in exchange for them giving up their nukes.