So, the Russians annexed the base in Sevastopol, and not the rest of Crimea. Jeepers, you guys just never give up.
The Russians deployed forces around Crimea to secure their base after the democratically elected government in Kiev was overthrown. They chose to do so in a discreet manner that preserved civil order and saved lives, while waiting for the western 'democracies' to regain their senses and force the Maidan radicals to return to the February 21st agreement that had just been negotiated.
They acted with restraint and in accordance with the status of forces agreement they held with the old government. Once it was clear the old government wasn't coming back... all bets were off.