Europe was supposed to have consigned national minority questions to history. A spat between Hungary and Slovakia over the last few days, slight in itself, shows otherwise. It illuminates a wider trend: Europe’s peace-building project is flagging, just as the issue of national minorities is returning on the continent’s borderlands.

On Monday, Slovakia’s ambassador was called in by the foreign ministry of Hungary, a fellow EU member, to explain why Slovakia had refused entry to Hungarian President Laszlo Solyom a few days earlier, turning him back as he crossed the Danube to the Hungarian-speaking town of Komarno.