Russia and Ukraine

[Thumpalumpacus]

Because there was no written legally binding agreement that NATO would deny sovereign states the right to seek protection from potential Russian aggression

Not to mention - but I’m going to anyway - the fact that Russia is signatory to a charter that recognizes the right of countries to choose their own security arrangements and alliances.

Boru

There's also the Minsk Accords, wherein both US and Russia are bound to provide for Ukraine's security. Of course Bel doesn't mention that.