I find the whole situation a little perplexing, to be honest, especially Putin's motivations and intentions. Perhaps someone familiar with Russian foreign policy could explain it to me but it just seems to me that Russia is grasping on to a by-gone era of imperialism.
Hopefully, Putin will realise what's good for him. If not, I can only hope the President gets serious about the consequences. Right now, he's very wishy-washy on what we're doing.
Honestly, the world has no clue what Putin wants out of this. I think it's about his ego. He lost Kiev, so now he's making life miserable for the new government there. He may even want war as an excuse to annex most or all of Ukraine.
Putin wants sevastopol port
The Russians have to ask the Ukrainians for permission to use this port, they get a lease on it - they literally "rent" it.
This wasn't difficult with a pro-Russian president in Ukraine, however the Russians are very worried now, because there's been an uprising in Ukraine, and the pro-Russian president was turfed out, they may lose their lease on this port
If they lose the lease, they lose their power in the region. Putin is a very clever man, he knows that he can push a certain amount and there won't be any military repercussions - no one is going to risk a massive war - so in a way he's playing a game of bluff, he'll push forces into Crimea, take Sevastopol all for himself - it'll cost Russia money and international relations - but he obviously thinks that the gamble is worth it to control such a vital port
He doesn't have any strong opposition at home (running in opposition is "difficult" in Russia) and he pretty much runs the media - so he can convince the Russians at home, and those in the Ukraine that he is merely trying to protect them - this is something a lot of them believe
this is a hostile take-over, internationally it's condemned, but to Putin, that naval port permanently in the hands of Russia is worth it