If the events in Ukraine are to appear as more than a series of disconnected events, you really must take the long view. So if you want to understand why it looked last night as though war was about to  break out in the Crimea, perhaps take a look at this piece of analysis by Stratfor. It's a company that focuses on geography and history to explain what is happening in the world. Stratfor makes its money by signing up paying subscribers, but makes some of its work freely available. The book from which this is taken, The next hundred years, is also worth reading. 

How to understand what's going on in the Crimea