On a cold Christmas Eve in Belgium in 1914, the sound of singing floated from the trenches where soldiers were dug in. Strains of the carol “Silent Night” rang out in German and then in English. Soldiers who earlier in the day had been shooting at each other laid down their weapons and emerged from their trenches to shake hands in the “no man’s land” between them, exchanging Christmas greetings and spontaneous gifts from their rations. The ceasefire continued through the next day as the soldiers talked and laughed and even organized soccer matches together.

The Christmas Truce of 1914 that…