Russian President Vladimir Putin told a televised press conference on Thursday that he doesn't want to send Russian troops into eastern Ukraine, where there is ongoing violence between Ukrainian government forces and pro-Russian separatists, but that he will invade if he has to. Though Russia also signed on to an international agreement to peacefully end the crisis, even President Obama seemed skeptical, saying of Moscow's promises, "I don't think, given past performance, we can count on that."
A full-on war between Russia and Ukraine is probably still not the most likely outcome of the crisis, but when a head of state publicly announces his willingness to invade a neighboring country, it's a pretty big step in that direction. And it's one of several indications this week that war is looking, while far from inevitable, increasingly plausible. Earlier on Thursday, as Russia and the US ostensibly reached a peace deal over the crisis, 300 pro-Russian militiamen attacked a Ukrainian military base.
Here are the four most likely outcomes of the Ukraine crisis, how they'd happen, and what makes them real possibilities. You'll notice that three of them end with some sort of a Russian victory over Ukraine: the best-case scenario for Ukraine and the West is the status quo, and that doesn't look particularly likely.
1) Russia annexes eastern Ukraine, without full-blown war
It's not clear whether Russia actually wants to seize eastern Ukraine, or is just bluffing to try to force the Ukrainian government to accept Russian demands. Analysts tend to lean toward "just bluffing," but in either case Moscow appears to be engineering a situation in which it could annex that territory.
The Russian playbook in eastern Ukraine appears to be this: instigate local separatist forces who will seize government areas and send in Russian commandoes, posing as local volunteers, to bolster them (this is what they did in Crimea). Simultaneously warn Ukraine not to use force against the separatists while putting Ukraine in a position where it has to use force against the separatists if it wants to keep control over its own territory. Mass Russian troops on the border and issue lots of subtle threats about how you might have to intervene if the violence you helped to instigate spirals out of control.
This is where we are now: three pro-Russian separatists were killed in overnight fighting. This forces Ukraine to either give up and accept Russia's demands (more on this below), or try to re-take its eastern regions by force, which could give Putin the excuse he wants to launch an invasion.
If Russia does invade, its military is so much stronger than Ukraine's that it seems likely that Ukrainian forces will simply pull back, as they did in Crimea. That would mean a Russian-occupied eastern Ukraine, which could well end with Russia annexing the territory through a Crimea-style rushed-through referendum. But it's also possible that Ukrainian forces would stand and fight, or that the situation would slip out of control, and that could mean open war.
2) Open war between Russia and Ukraine
Again, this is probably not the most likely outcome — principally because no one wants it to happen — but it is possible. Here's why: pushing the Ukraine crisis nearer to the point of war is precisely the threat that Putin is using as leverage. That leverage is sufficient enough that he's winning right now. But if he pushes harder on it, the risk of war actually happening increases, whether he wants that outcome or not. That's particularly true if Russian troops move in to "protect" the Russian-speaking separatists from Ukraine's crackdown, as Moscow has been implying it would.
As far as casus belli go, it would be far from history's flimsiest or most transparent. In 1830, French King Charles X justified his invasion of Algeria as punishment for the Algerian leader having slapped the French consul with a fan — three years earlier. In 1931, right-wing elements in the Japanese military bombed a Japanese railway in the Chinese province of Manchuria, then blamed it on local insurgents to justify a full annexation of Manchuria. In 2003, the US invaded Iraq to dismantle weapons of mass destruction that turned out not to exist.
None of those conflicts ended well. A Russian-Ukrainian war would probably be much, much briefer, since neither side appears to really want it to happen, but conflicts can be unpredictable.
3) Ukraine would adopt a federal system to appease Russia and end the crisis
This appears to be Russia's preferred outcome: to have Ukraine change its government to a federal system that would give more power and autonomy to individual provinces. Ukraine may ultimately feel it has no choice but to bow to this demand, in which case those separatist forces would likely stand down.
The reason Moscow wants this is that, in the current system, Ukraine's pro-Western government might not be very inclined to cooperate with Moscow. In a federal Ukrainian system, regional governments will have much more autonomy and power, meaning that Moscow can get what it wants by simply calling up pro-Russian regional governors in Ukraine's typically pro-Russian east.
These eastern regions have lots of important natural resources like coal. They also have factories that produce essential military equipment for Russia. So if Russia can count on keeping them solidly pro-Russian by forcing Ukraine to adopt a federal system, that may well be enough to appease Moscow. This could ultimately worsen Ukraine's already-severe political divide between west and east.
4) Status quo: Russia backs down and nothing major changes
It is certainly possible that Ukraine will be able to rout the pro-Russia separatists without major incident and/or that Moscow will decide it's better off backing down. Maybe the risks for Russia will come to outweigh the benefits — particularly if the European Union credibly threatens broader economic sanctions — and Putin will decide to focus on preserving what he's won already, namely Crimea.
This outcome is the premise of today's big international talks between Russia, the US, and others in Geneva. As part of the agreement, Ukraine promised amnesty for any fighters if they leave the government building they're currently occupying. But the separatist fighters are still there, as are the thousands of Russian troops massed at the border. Unless the US can get Europe to threaten some more severe sanctions — which Europe is hesitant to do because of how much it would cost them — Moscow has little incentive to give up a fight that it is currently winning.