Ukraine now looks all but certain to be torn apart, with the Crimea and parts of eastern Ukraine falling under Russian domination.
Russian President Vladimir Putin has all the power, and all the skills, to accomplish this if he wants to. And it seems he probably wants to. The chief question is whether this will be achieved relatively peacefully, or with substantial bloodshed.
But there are tough lessons to be learned here too about the international order.
In what he regards as Russia's near abroad, particularly those nations such as Ukraine that were once part of the Soviet Union, Putin will do what he wants on the basis of pretty flimsy pretexts.
He is not scared of incurring Washington's displeasure; he seems to delight in humiliating Barack Obama. And he just laughs at any threats the European Union makes.
The fate of Georgia, a slab of whose territory and population is now permanently under Moscow's control, and the likely fate of Ukraine, demonstrate the problematic, if not downright foolish, way in which the US and Europe, through NATO, have provided security guarantees, and promises of security guarantees, to nations right up to the Russian border.
The truth is that no West European, and no American, is going to die protecting the borders of nations that abut Russia. Increasingly, Putin is inclined to call this Western bluff, just as he has done so shamelessly in Syria.
The international law aspects of the case are messy too. The Americans point to the irony of Russia so often extolling the importance of national sovereignty yet blatantly intervening in Ukraine.
Yet the Russians claim that the international responsibility to protect doctrine allows them to protect Russians inside Ukraine, although in reality no ethnic Russians in Ukraine have been in any danger.
But while Viktor Yanukovich was a corrupt and hopeless Ukrainian leader, he was democratically elected, which offers Putin plenty of fig leaf.
The US and Europe cannot provide Ukraine with security. They can provide aid and hopefully get the western remainder of the state on to a path of economic reform and modernisation.
In the meantime, avoiding bloodshed is a legitimately high priority.