The madness that saw millions of young people go out to slaughter each other on the battlefields of the First World War started 100 years ago today.
Of course, on all sides, most were motivated by high ideals: to defend their country, to right a wrong, to do their duty. Killing people who had precisely the same motivations. All egged on by the same destructive nationalism and its remorseless logic.
Few, when it started, realised the scale of the forthcoming massacre that would wipe out half a generation across Europe. Many thought they would be home by Christmas, returning as heroes. Instead, all too many perished in the most atrocious conditions.
At that time, of course, there was no European Union, with national leaders meeting six times a year to reconcile differences, with its elected parliament to develop a culture of debate and mutual understanding, with its common market to deepen common interests, with its court to settle legal disputes, with its student exchange programmes bringing young people together to study, not to fight.
For all its faults, the European Union has been a key factor in securing peace in Europe. A return to the old system of rival sovereignties, shifting alliances, with no cooperative framework to bind us together, which some old-fashioned nationalists seem to want, would be a disaster. We must not let it happen.