Christmas 1914, flooded ditches in front of Ypres. The war is four months old and already industrial. Somebody starts singing. The other side answers. Men crawl up, shake hands, bury the dead, trade buttons. A ball appears.
Why then
Volunteers and conscripts on both sides still know the same hymns. The front has frozen into mud but not yet into a four-year system. The calendar sets it off: a carol on a cold night.
What they wanted
The men want a day without killing. High commands on both sides need the war to keep running, and they see the danger at once: a soldier who has met the enemy may not shoot him.
What changed
The truce is suppressed, punished, then mythologised. By Christmas 1915 the guns have orders to fire through the holiday, and only small truces flicker. It ends nothing. It shows the exit nobody in command would take.
Still argued
The evidence is the letters men wrote home that week, and they describe something real. How many sectors joined in, how much football was played and how much was added later are still argued.