At the end of World War I, Winston Churchill watched Europe rise from beneath the floodwaters, its borders redrawn, its monarchies toppled. One soggy patch of soil, however, had not changed. “As the deluge subsides and the waters fall short, we see the dreary steeples of Fermanagh and Tyrone emerging once again. The integrity of their quarrel is one of the few institutions that have been unaltered in the cataclysm.”

Exactly a century later, as the pandemic recedes, Northern Ireland is again locked in its ancient quarrel. This time, though, that quarrel has the capacity to wreck relations between the United Kingdom and the European Union, and so cripple the Western alliance.