Don't totally agree with the analogy. It think Crimea is strongly pro-Russian and would voluntarily split with Ukraine and join Russia given the opportunity. I'm not advocating Putin's actions, but I don't quite see the Crimeans as being coerced.
Also, Russia has Black Sea access in the Southern state. Sochi being at the far end of that coast. Though it is a little further away and with limited overland transportation options, that hardly seems like a reason for invading. Far less costly to develop overland transport, if they haven't, than what's happening. I just don't think that's the reason for the current invasion.
I think Putin, and to some extent the Russian people, want to re-establish the Russian empire and prestige. With such a weak and sissified US President a power vacuum has been created and nature abhors a vacuum.