VIENNA — As Russian leaders, diplomats and commentators ponder the division of Ukraine, we must begin to ask what this would actually mean.

If the present crisis ends with the fragmentation of the Ukrainian state, the result will be disastrous for all concerned, including Russia. The risk is that, in conditions of chaos and in the absence of a decisive Western stance, Russia could follow the logic of its current commitments to a very dangerous conclusion.

Unlike Europe and the United States, Russia has a clear stance on Ukraine. Vladimir Putin’s hope for the future is his Eurasian Union, to be established next January as a rival to the European Union. Belarusian and Kazakh strongmen are game to join his dictators’ club. But since the idea has little popular support anywhere, Eurasian integration can take place only in conditions of Russian domination and local dictatorship. For Mr. Putin, the Eurasian Union would be meaningless without Ukraine. Eurasian ideology is the brainchild of Alexander Dugin, who has never disguised his admiration of fascism. His website publishes Russian strategists who claim that Ukraine is not a sovereign state.

The current crisis in Ukraine began because of Russian foreign policy. The Ukrainian government, led by Viktor Yanukovych, seemed poised to sign a popular association agreement with the European Union. Mr. Putin jumped in quickly with cash and low gas prices for Mr. Yanukovych, who then abruptly changed course, refusing to sign it. Because Mr. Yanukovych’s family has amassed unbelievable wealth during his presidency, he might also have been concerned about the possibility that the European Union would bring the rule of law. This would not be a risk in the Eurasian Union....