PLOEGSTEERT, Belgium – With British and German forces separated only by a no-man’s land littered with fallen comrades, sounds of a German Christmas carol suddenly drifted across the frigid air: “Stille Nacht, Heilige Nacht” (“Silent Night, Holy Night”). Then, during that first Christmas Day in World War I, something magical happened. Soldiers who had been killing each other by the tens of thousands for months climbed out of their soggy, muddy trenches to seek a shred of humanity amid the horrors of war. Hands reached out across the narrow divide, presents were exchanged, and in Flanders Fields a century ago, a spontaneous Christmas truce briefly lifted the human spirit. “Not a shot was fired,” Lt.