So Ukraine had internal political disagreement connected to whether it wanted to join the EU or Eastasian Union. It's former leader sided with the latter, the public in the western Ukraine largely said no, there were riots and killing, then Russian invaded because it saw opportunity.
The key in all of this are Russia's intentions. Do they want to seize Crimea as they have, or is this an attempt to annex the Russian speaking part of Ukraine as a whole?
If Russia is demonstrating it's capability and tomorrow they will suddenly withdraw, we will avoid war but create a new Cold War conflict line between Russia and not-Russia.
If Russia is annexing Crimea, war may be avoidable and negotiated settlement possible, which could include referenda and the like. Tricky, but it would avoid bloodshed.
If Russia wants to annex Russian Ukraine, and is aiming to do so, then war is likely in Ukraine.
Under Putin, Russia will to do as it pleases because it cannot be challenged without inviting the set of risks that came with the Cold War.
This is not a viable option for most, including me. The long game could be catastrophic.
So what then for the rest of the world? Let Russia do as it pleases for the next years or decades until its internal politics finally change? Or, muck about at confronting it rhetorically and maybe militarily?
Scenario: Russian annexing of Ukraine makes Obama look weak to US voters. The TeaGOP then wins the next US election with a name-your-swaggering-blowhard at the helm...
Aside: This is the kind of thing intelligence agencies should be all over, not snooping on ordinary people who don't like pipelines and oil tankers.