Russia would not be the first former empire to face a moment of historical reckoning. Spain’s 1898 defeat at the hands of the upstart Americans was a watershed moment in Spanish history. The global empire that had defined Spain since the voyages of Columbus had suddenly disappeared, and Spaniards began to question everything from the monarchy to the role of the church.

For Britain and France, their ignominious failure in the 1956 Suez campaign forced both countries to realize that they were no longer independent global powers. The glories of empire were over, and the two former superpowers began, painfully and reluctantly, to adjust to their new circumstances.

A decisive Russian failure in Ukraine could be Moscow’s Suez moment. If Russia fails to conquer the heart of Ukraine (western Ukraine is less of a concern in Russian historical mythology), Russians will be unable to avoid the conclusion that the empire of the czars, painfully assembled over many centuries and restored by Lenin and Stalin after the disasters of World War I, has irrevocably fallen. This will force the kind of deep introspection in Russia that other former empires have had to face. The consequences will be far-reaching…

Worse, perhaps, from the viewpoint of the “Eurasian” theorists and radical Russian nationalists who provide a veneer of legitimacy for Mr. Putin’s regime, a victory for Orthodox, Slavic and democratic Ukraine over despotic Russia wouldn’t only challenge the personal legitimacy of Mr. Putin. It would challenge the idea of Russian exceptionalism and fatally undermine the view that despotism is the form of governance best suited to the Russian soul.