Who is to blame for the crisis in Ukraine: Russia or the United States and Europe? A lively debate on the question resurfaced lately, but it has a vital flaw in that it fails to consider the roles of the countries caught in between.

It's as though Churchill, Roosevelt and Stalin were back at the negotiating table in Yalta, carving up Europe. Only this time the issue isn't whether Stalin got to impose regimes from Warsaw to Sofia, but whether President Vladimir Putin has a right to impose them from Ukraine to Kyrgyzstan.

John Mearsheimer, a professor of political science at the University of Chicago, has argued the "we're-to-blame" position most cogently. He makes what he calls a realist case for the inevitability of Putin's response to decisions of the North Atlantic Treaty Organization and European Union to absorb the ex-Warsaw Pact countries, followed by the three ex-Soviet republics in the Baltics, and then to flirt with Georgia and Ukraine. The attempt to turn Ukraine into a "Western bastion," he says, was a final needless provocation.