As someone who lives on the other side of the world and has no bias to either side, this is what I read between the lines. Since the end of the cold war, Russia and the US(through NATO) have been fighting for control(through trade and arms/military agreements) of the countries in the old east block, US got Lithuania, Latvia, Estonia, Romania and everything west of them, Russia got Ukraine and Belarus, probably some around the mid-east (Kazakhstan etc).

Now many years have past, things are settling down, Russia and the west are getting along very nicely, both side are living similar lifestyles, most animosity has gone (remember soviet Russia jokes?). The usual economic wars have not stopped but are played by all counties (from China to Brazil).

Meanwhile in Ukraine the difference between east and west has become blurred, it is the new front for economic and military control. Now if you want to lay blame on why this is all happening you would look at all the old people who lived through the cold war. The senators who couldn't let it go, the new generation has pretty much forgotten about this old fight.

Anyway so the CIA moves into Ukraine to battle the FSB(new KGB) and they start stirring up shit. CIA wants pro-EU presidents, FSB wants pro-Russia presidents, they both organize protestors, escalate the protests, eventually push them to violence. People don't just start a civil war over what country they are buying their gas from, this is outside forces tearing up the country, now NATO has it's foot in the door to Ukraine.

From a non-nuclear military standpoint, Russia needs both Belarus and Ukraine to defend the large flat plains of ground (you can see in the south they have the mountains before Georgia) so as long as Belarus and Ukraine where under Russian control they never had to make a military move, they where 'buffer states'. But western Ukraine becoming more positive to NATO changes all of this.

So the Russians hand has been forced, they secure Crimea, propaganda on both sides call it "Liberate/Annex", there is a rebel situation in eastern Ukraine that Russia helps so it still has it's foot in the door.

So now here we are at this standstill, in a way US/NATO has already won, they have created mass pro-western sentiment in the west and Russia will no longer be able to control the whole country. Russia could storm the whole country but probably suspects that will give real legitimacy to NATO, as they have been operating mostly in the shadows. I don't think Russia will want to annex the eastern part of Ukraine, as it needs the entirety of Ukraine as it's buffer state and will decrease the number of pro-Russian Ukrainians. Crimea was more of a "if it all goes to shit as least we still have Crimea, and important military location". If either Russia or NATO employs full deployment the country will probably be split in two.