What's the big deal? Opponents of the Crimea vote like to point to the illegality of the referendum. But self-determination is a centerpiece of international law. Article I of the United Nations Charter points out clearly that the purpose of the U.N. is to "develop friendly relations among nations based on respect for the principle of equal rights and self-determination of peoples."
Why does the U.S. care which flag will be hoisted on a small piece of land thousands of miles away?
If you read most mainstream news coverage of the Crimea referendum, you've probably heard about the 97%+ vote in favor of joining Russia, and how the vote was probably rigged or otherwise influenced by the occupying Russian army. Ron Paul argues that the illegitimacy of the vote shouldn't matter:
Critics point to the Russian "occupation" of Crimea as evidence that no fair vote could have taken place. Where were these people when an election held in an Iraq occupied by U.S. troops was called a "triumph of democracy"?
Just, wow, holy shitballs, where to start...
Yes, both regions were occupied by a foreign invader. Here's the differences:
(1) Iraq was being asked to whether or not to become a member of the nation that just invaded it.
(2) The options in Iraq weren't, "Would you prefer to be ruled by a governor appointed by George W. Bush, or to break into half a dozen smaller autonomous nations?"
You see, in the Crimean referendum the choices were only to join Russia or to become autonomous. The decision to maintain the status quo as part of Ukraine was taken off the table, which is why the vote was so skewed towards joining Russia -- people who wanted to stay in the Ukraine decided not to vote as a form of protest.
Now all that aside, there still is the question why we should care if people decide to secede from their nation. And to answer that question we can go back 150 or so years to Abraham Lincoln and the years leading up to the Civil War.
In numerous speeches Lincoln talked about preserving the Union, and the reason wasn't just that the United States is so awesome. To Lincoln the preservation of the Union meant something much greater, it meant the survival of democracy and the rule of law. If secession became the mechanism by which nations resolved major disputes the nation would soon fall completely apart. The North and South would split, then New England may split from the rest of the North (an idea that had been contemplated there before the war). Rich areas would secede when they decided they didn't want to support poor areas. States would split off over abortion, the death penalty, health care, social security, war votes, defense spending, any number of things. With more small nations with competing interests we'd see the kinds of local conflicts predicted by the authors of the Federalist Papers, and we'd devolve into warring city states until an authoritarian empire invaded.
That's why we care about self-determination going to the point of secession.
Now we are engaged in a great civil war, testing whether that nation, or any nation so conceived and so dedicated, can long endure.