Europe's medieval map: As the EU unravels, the continent is reverting to divisions that go back centuries

Europe thus now finds itself facing an unhappy historical irony: The decades in which it was able to develop its high ideals of universal human rights, including the right of the distressed to seek havens in Europe, was made possible, it is now clear, by the oppressive regimes that once held sway on its periphery. The Arab world was slammed shut for decades by prison states whose dictator-wardens kept their people in order. Saddam Hussein in Iraq, the Assad family in Syria, Muammar Qaddafi in Libya—they allowed Europe to have its idealistic cake and eat it, too.

Worse for European unity, geography and history have conspired to make some regions of the continent more vulnerable to the flood of migrants and refugees than others. As Germany and parts of Scandinavia lay down a very tentative welcome mat, Central European countries like Hungary and Slovenia erect new razor-wire fences. The Balkans, virtually separated from the rest of Europe by war and underdevelopment in the 1990s, have now been dealt another blow by the anarchy in the Middle East. At the southeastern extremity of Europe, Greece, once a poor Ottoman province, has seen its economic crisis exacerbated by its unlucky position as the gateway for hundreds of thousands of migrants fleeing the Arab world’s turmoil.

Another critical factor in the period of relative stability now coming to an end in Europe was the geopolitical role played by Russia. During the Cold War, the Soviet Union was an obvious strategic threat, but it was a threat well-managed by the U.S., and for most of the period, after Stalin’s demise, the Kremlin was led by stodgy, risk-averse functionaries. After the Soviet collapse, a decade of turmoil and institutional weakness in Russia meant, among other things, that it was no threat to Europe.