Ian Welsh makes the argument that Ukraine is next on Russia's shit list. The question you've got to ask, before you start screeching about how we've got to protect the territorial sovereignty of our ally (?) Ukraine, is whether or not it's worth going to war with Russia, or even putting up a significant deterrent (>10,000 men) in order to prevent war, over a province that's historically Russian, filled with Russians who don't want to be Ukrainian, and that we generally don't give a fuck about.
This is the Kosovo Precedent, people. You want to keep Ukraine's current borders? Then pony up. And if you can't stomach a years- to decades long involvement in Russia's southern flank, then there's going to have to be stuff you just accept.
The closest comparison to the mess of problems in the FSU is the fall of the Russian, Austro-Hungarian, and German empires at the end of WWI. These empires had significantly mixed ethnic populations, so when the empires collapsed various new nation-states found themselves with substantial pockets of minorities, some of whom liked to make trouble, and some of who just though the mapmakers in various European capitals shouldn't get to decide which country they lived in. The only solution was WWII, during which atrocities throughout the period sent massive population flows heading east and west and effectively balkanized central Europe in a way it hadn't been before.
Hopefully, there's a better way to do this today.