The current dispute developed as the re-emergence of an internal struggle for power between the pro-Russian and pro-European forces within the Ukraine. The first climax of this battle occurred in the so-called Orange Revolution of 2004-5 (called so because of Agent Orange, the dioxin-based chemical with which the pro-European candidate Viktor Yushchenko was poisoned, but not killed). Protests overthrew the rigged election and Yushchenko won the rematch. The balance tipped in the other direction, though, and Yushchenko and his one-time ally Julia Timyoshenko fell from power. The other V.Y. of the 2005 election, the pro-Russian Viktor Yanukovich, won back the Presidency in 2010, Timyoshenko was imprisoned and Yushchenko marginalized.
Yanukovich negotiated with both the EU, who offered aid and a path toward eventual associate membership, and Russia, which offered debt relief and natural gas. It should come as no surprise that Yanukovich took Russian President Putin's best offer last fall, but the Ukrainian-speaking portion of the population (a narrow majority) took umbrage and began a continuous protest demonstration in Kiev, the capital. The demonstrators were led by Vitaly Klitschko, the former heavyweight boxing champion and one of the truly outstanding figures of the current era: Klitschko was probably the greatest heavyweight of the last 20 years--his only true rival was his brother, Wladimir, who's now the champ--he has a Ph.D. (the only boxing champion with that credential), and has acted thoroughly responsibly throughout the crisis. I would say it is a high probability that he will emerge from this crisis--assuming Ukraine retains its sovereignty--as the future leader of the country.
In the meantime, though, the demonstrations began to get violent, people began to get killed, and both sides took up arms in the capital. Yanukovich turned loose snipers who killed several dozen one day in an attempt to suppress his opponents, but it did the opposite. The people in Kiev rose up as one, chased Yanukovich's people out of town and into hiding, and put him on the run. The Ukrainian Parliament voted unanimously to strip Yanukovich of his position, there was discussion of trying him for crimes against humanity, and an interim government was set up.
In the aftermath of the coup, there was peace in Kiev, but an unstable security situation in the Eastern provinces, which are predominantly, or overwhelmingly, Russian-speaking. Both sides were calling the other fascists and other names. There was a faction there calling for splitting the country and reuniting the Russian part with Putin's country, but most were not going that far. Yanukovich made noises from Moscow, then started coming closer to the theater of action; the Russians announced military maneuvers on the Ukrainian border.
Then things really heated up, with pro-Russian paratroopers appearing overnight and taking up positions to control both airports on the peninsula of Crimea. Crimea is the weak spot in the argument for Ukrainian sovereignty: the Russians have a legitimate lease for its navy to use the Crimean port of Sevastopol for decades to come. Timyoshenko has made noises in the past about revoking the lease--this and recent developments have made the Russians nervous. Crimea is also overwhelmingly Russian, and its being a part of the Ukraine is an artifact: a gift made from the Russian Soviet Republic to the Ukrainian one back when Nikita Khrushchev (a Ukrainian) was the dictator of the USSR, something that was never reversed, survived the breakup of the Soviet Union, but now looks like a mistake.
Some things seem to stay the same, beyond the bounds of time. Crimea was the site of a two-year war between Russia and the Ottoman Empire (Turkey) from 1854-1856, with the French and British backing up the latter, over Russian access to warm water ports. * Ukraine was part Austria-Hungary, part Russia then--there was no Ukraine. I leave it to you to look up the history; preferably one that looks beyond just the British involvement. I will point out that the famous suicidal charge of the Light Brigade, immortalized by the English poet Lord Tennyson, was in Balaclava, which is the English word for the face masks worn by the Russian paratroopers this week.
Yes, the Russian ones. The Russian Parliament has given its backing to Russia's use of its military to defend its interests in Ukraine (after the fact). It is an aggression, probably modeled after the one in the former Soviet state of Georgia a couple of years ago when that country did not behave like one should within the Russian sphere of influence. As with Georgia, Russia has some legitimate claim to interest itself, though it has gone beyond that in its de facto takeover of the peninsula. Putin seems to be developing something of a Monroe-like Doctrine in asserting some right to interfere in the affairs of ex-Soviet republics (though Russia has let go completely of the Baltic Republics, for which the Soviets' claim was always suspect; the three Baltic states have already joined the EU). The US had the advantage of being the only power in the hemisphere when Monroe issued his, though, and in this case the EU is the counterforce in the neighborhood. The EU is acting in a coordinated fashion, and this episode may prove that the EU can successfully conduct a meaningful foreign policy. This is not a UN thing; though the Security Council may discuss it, heatedly, no resolution would ever get past a Russian veto.
The Ukrainians are tolerating the Russian presence in Crimea, so far, but will clearly look to draw the line there; they have ordered a general mobilization and look prepared to fight the Russians if necessary.The US has been a bit of a provocative influence, openly helping the pro-European side. I have seen more than a few nuts on the Internet talking about this sparking WWIII (and Obama handled one such person who sought to heckle his speech today). Those folks are so passionate in their opposition they wish for the worst, just because it will make Obama look bad. There is a real risk of US-Russian relations re-freezing into something like a new Cold War, if the Russians do not stop at Crimea, though I think they will. I presume that Yanukovich and his band mean nothing to Putin, and he would only lift a finger to help them if it's purely in his own interest. I could see the possibility of a referendum in Crimea, which would probably go the Russians' way, so they can probably get what is most important to them without further aggression, and there might even be a couple of other provinces that need to reconcile their Russian majorities to continued presence in the Ukrainian state. Meanwhile, the US should back off, except to offer natural gas (liquefied, in this case) at a decent price, so that the Ukrainians are less subject to Russian extortionist terms.
Speaking of Splitting Up Countries...
After the tumultuous series of events in the late Eighties and early Nineties which started with the Berlin Wall's fall and ended with the settlement of the conflict in Bosnia, Europe experienced a period of relative peace and stability of borders. As with Africa, it's generally considered to be better to let the borders be, even if they aren't sound from the point of view of politics, culture, or language, rather than open up Pandora's Box. In that regard, the splitting of Sudan and the creation of South Sudan in 2011 might signal a new round of shifting borders, with Crimea being the next.
There are more possible adjustments on the horizon. Most notably, the Scottish have a referendum this September on separation from Great Britain. Conservative British Prime Minister David Cameron promised them the referendum in the last electoral campaign in 2010, and now that promise has come due. It is perhaps surprising that the drive for independence (after some 400 years of union) is so strong, but the British parties are all pleading to the Scots to stay around (Labour and the Liberal Democrats would lose significant ground nationally without them, while the Conservatives would be the goats, reviled through history for giving up Scotland)--and there is some threat about taking away their access to the British pound (of which they are very proud and fond). I think this is a good time for the Scottish nationalists to make a deal with the British, but they seem very stubborn about wanting their vote--which I think will fail in the end if it comes to that.
Then there is Catalonia--the Catalonians have been making noises about a referendum (the planning is for 2015) on splitting away from Spain, and there is currently a pro-independence majority in the Catalonian regional government. This does not mean that Catalonia is about to become a separate nation, though. The Spanish central government has said that it would not allow such a referendum, and it is not clear it would have a chance of passing. Most likely, Catalonia would be more than happy with an expanded degree of autonomy such as the Spanish Basques got--and appear to be more than happy with, after all that bombing and rebellion and such.
* I should acknowledge the article of my neighbor, the Corriere della Sera (their offices on via Solferino are about three blocks from my current home), which pointed out that the nascent Italian Kingdom under Count Cavour of Savoy also sent several thousand troops to the Crimean War during the tail end, which earned it a spot at the negotiating table and some prestige for their ongoing attempts at making a nation (English translation on the link is automatic, but weak).