Russia did invade, they annexed Crimea in 2014. Which in hindsight seems more like retaliation for the coup. To me Russia's responses are based in a timeline of years. USA helps install a pro west government in 2014, Russia takes Crimea. Then Russia waits and sees if Ukraine gets "the message".

An election cycle later and the pro west government still sits in power and is now talking about joining NATO. What does Russia do now? They increase their "messaging". They invade the eastern border and probably will attack the capital in response.

Don't get me wrong, I'm pro west on this issue. Despite all the flaws of the USA and the west I still believe that western political society and it's ruling class are preferable to the Russian's version. But I can understand were Russia would be coming from. I'm sure if say...Cuba was to join a military alliance with Russia (or China) and they started placing military assets (Like missiles) into Cuba's territory we might just find ourselves in a near world ending scenario... again...

Russia doesn't want a western military ally right on its border any more then the USA would have a Russian ally right next to them.