It's interesting. Russia does nothing more than sort of mumble in protest as we sign up nation after nation in their neighborhood into our military alliance. NATO is not a boy's club, you know, nor is it an economic organization. It is purely a military alliance, providing for commonality of weaponry and military practices. Russia expresses discontent but does not even make formal protest in the UN as, one after another, we sign up its former allies (satelliet nations) into our military alliance.
But then, when we reach the final ones and attempt to sign up the nation that is actually on their border, their equivalent of what Canada or Mexico would be to us, they say "Oh hell no," and we label them as agressors. They stop our military advance on them and so they are the agressors.
You did know, didn't you, that the "economic aid package" which Ukraine turned down from The European Union included requiring that Ukraine adopt NATO weapon standards and convert their military within a few years. Aside from what that would cost Ukraine, and the profit it would involve for Europe and the US, it was a military incursion into Ukraine; an attempt to make the Ukranian military part of NATO. A reasoning person might see why Russia would object to that.