Putin's motives and actions have been cloaked in a fog of political confusion and media alarum. Here is a piece, the first I've seen, that makes some sense about what has happened in the Crimea.
One item: "Safeguarding this maritime muscle [navy base in Crimea] may well have been one reason President Vladimir V. Putin of Russia sent armed forces to seize Crimea. But is it possible that the Sevastopol base is just the most concrete manifestation of Russia’s deep interests in Ukraine that the United States and its NATO allies either ignored or forgot as they tried to bind it more tightly with the West?" NYTimes.
Have you seen stories that throw light on Ukraine, Russia, etc?
UPDATE: Here is William Pfaff (corrected link) in CWL on why Putin has gone as far as he will go. Too Sanguine?