WHY IS IT that John Mearsheimer, a distinguished American exponent of international relations, has reached such an apparently perverse conclusion about Russia’s “special military operation” in Ukraine? It is a “special military operation” indeed—one whose initiation and conduct have been condemned as violating the most fundamental rules and norms. Yet he argued in an article for The Economist’s By Invitation section on March 19th that “the West, and especially America, is principally responsible for the crisis which began in February 2014.”

Professor Mearsheimer does not let Vladimir Putin off the hook entirely: “There is no question that Vladimir Putin started the crisis and is responsible for how it is being waged,” he writes. But Professor Mearsheimer’s central argument is that the crisis began at NATO’s Bucharest summit in April 2008, when President George W. Bush, along with the other NATO member states, ostensibly committed the alliance to the future membership of Ukraine and Georgia. The Russian leadership was deeply opposed to the prospect of NATO extending its reach so close to the heartland of Russia.

It’s questionable whether Mr Putin was right to say NATO posed a threat to Russia’s sphere of influence. From the start in 2008 there were different interpretations of what was meant by “will become members”. For some these words, with no time-frame specified, were there to enable President Bush to return home from Bucharest with something to show for his trip. Other member states, all of whose votes would have been essential for any formal offer of membership, remained doubtful. But Mr Putin took the phrasing seriously.

Professor Mearsheimer’s argument has some strength in suggesting that the 2008 Bucharest summit declaration was a disaster. He has shown consistency in this matter. He practically invented a school of international relations called “offensive realism”, based round the idea that systems in which there are several great powers are prone to manage their mutual relations with deep rivalry and a high risk of war. One conclusion that follows from his world-view is that states are bound to take seriously the concept of “spheres of influence”, an old-fashioned term for a phenomenon that is still very much alive. However much spheres of influence may challenge the idea of the sovereign equality of states, they have by no means disappeared in international relations.

Take the 1962 Cuban missile crisis. In demanding the withdrawal of Soviet nuclear-armed missiles from Cuba, America was, in effect, defending the Monroe Doctrine of 1823. The doctrine sought to exclude European colonial rule and military presence from the western hemisphere. As for the Soviet Union, throughout the cold war it regarded virtually all of eastern Europe, where it imposed client regimes, as its sphere of influence under the euphemistic label of “commonwealth of socialist nations”.