Truth is NATO has broken agreement after agreement. It's all about Natural resources and terrain. Ukraine has the ability to cut into Russia's economy by selling oil to the rest of Europe. RUSSIA would not be able to survive. Also Crimea is costing Russia billions to supply water since Ukraine has cut off it's major water supply and Russia will not lose that Major port to the black sea. Finally Russia believes NATO is a hostile alliance and the terrain features that Ukraine has will help defend against any NATO ground offensive. Even in today's world terrain features go a long way in protecting nations from attack and or allow a nation to properly defend itself.