1) Crimea was handed over to the Ukraine in the 1950s. Before that it was Russian. Hell the people of Genoa have a better claim to Crimea than Ukraine (it was their colony for hundreds of years)
2) The population of Crimea is mostly Russian, speaks Russian and associates it self with Russia.
3) The Crimea has considerable self rule within Ukraine. This self rule has been under serious threat from especially the people behind the new Kiev government.
4) The new Ukrainian government claims a lot of things, but there is no evidence to back these claims up. And in some cases there is actually the opposite... as with this supposed threat from the Russian government to surrender.
5) The Ukrainians have tried many times go back on their deal with Russia on the Black Sea Fleet. Why is that?
Again how can you violate national sovereignty of a country in an specific area only, where you are the one that has always been in full control.. either directly or indirectly through local government that sympathises with you? You do realize that the government in Kiev has zero control over Crimea right, both before the crisis and now? The elected officials in Crimea and police/para military dont recognize the new Kiev government and feel very threatened by the rise of the new government, of which there are parts that are ultra nationalists and neo nazi.. please note I said some, not all. Considering the previous actions by these people in Kiev over the last 20 years, then I fully understand why the people in the Crimea feel threatened.So two wrongs make a right? Did you just admit that Russia did in fact violate Ukraine's national sovereignty?
Look at this way.. if say Texas was ordered by the Federal government to cede powers to Washington.. dont you think they would rebel also?