The Russians had said very clearly and specifically that they could not allow Ukraine to become a member of a hostile military alliance on their borders.

Now, you can argue that Ukraine in NATO does not pose an existential threat to Russia, but it does not matter one bit what YOU think - it only matters what the Russians think.

Likewise, I am sure the Russians could have argued that Cuba, as a sovereign nation, had the right to station Soviet ICBMs on its territory, and you would be technically correct, but the Americans didn't see it that way.

Also, if Mexico decided to join a mutual defense pact with Russia, and invited Russia to station their troops, weapons and missiles in Juarez and Tijuana, I am sure that the USA would say "NYET".

The fact is, Joshua, great world powers have "spheres of influence" - areas where they insist on having unquestioned and complete hegemony.

The USA defined their sphere of influence in the Monroe Doctrine - I suggest you Google it. The Monroe Doctrine declares that the Western hemisphere (North, South and Central America) is the inviolable sphere of influence of the USA, and no other world power may violate it or encroach upon it.

The Russians have the same idea when it comes to Ukraine.