If one looks at the map of Europe going back through time, Russia has been the ruler in Crimea for a great deal of that time. The only reason the EU wants it so bad is because of the gas lines. Period.
That is not the only reason that the EU is interested in both Ukraine and Crimea. Control of those two areas gives control of the Black Sea to whomever controls them. And control of the Black Sea by the EU would effectively throttle Russia's access to the world through the only warm water ports available to Russia. If Ukraine had become part of the EU, the EU with the help of Turkey would have effectively controlled the Black Sea, which would have been Putin's worst nightmare. Now with Crimea in Russia's back pocket again, even if the rest of Ukraine became part of the EU, Russia would still be in control of the Black Sea.
Tis a game of chess that the Russians will win, even though the EU will do its utmost (read this to mean war with Russia again) to stop the Russian bear. Only this time the EU will lose - Putin is pulling the strings this time and is anticipating an attack from the EU. Just look at how Putin is lining up the chess pieces and it becomes obvious that he EXPECTS retaliation and he is preparing for it.
Putin controls one third of the gas to the largest EU country (Germany), controls another large portion of oil with its support of Iran, and is re-conquering strategic territories lost during the USSR breakup. Who will be next after Crimea? Eastern Ukraine? Moldava? Lithuania/Estonia/Latvia? All of those territories are strategic chess pieces to Putin. He is likely to recover all of them. And all of them are adjacent to sea lanes to the outside world.
The only real problem Putin has is with the Turks, who hold the choke point between the Black Sea and the Mediterranean. He has two problems there. First, Turkey wants to join the EU. The EU does not want Turkey, but does want control of the Mediterranean which is impossible without the support of the Turks. Second, Turkey fears Russia. Turkey has a large minority population of Tatars and they remember what Russia did to the Tatars of Crimea (about 15% of the current population of Crimea) in the past. The re-conquering of Crimea has got to be sending shivers up the spines of the Turks.
What do I expect? Moldava, Eastern Ukraine, Estonia, Latvia, & Lithuania to again become part of the Russian beast. Western Ukraine to become part of the EU, but with few, if any, seaports on the Black Sea. Turkey to sidle closer to the EU, but not become a full-fledged member. Putin eventually tightening the screws to the EU resulting in a massive too-little too-late retaliation by the EU.
The U.S.? Nada, nothing, zilch. We don't dare do anything. If we do, Russia and China will dump the debt we stupidly sold them resulting in the destruction of our economy. If you have no money, you cannot fight, much less win, any wars. It seems obvious to me that both Russia and China have already communicated to us their intent to destroy our economy if we do anything other than whine and whimper while we pout.