Maybe My Favorite Christmas Story.

There's a story from WWI about British troops and German troops calling an "informal armistice" on Christmas Eve of 1914. German troops began by decorating around their trenches and singing Christmas carols. Most notably "Silent Night" or "Stille Nacht". British troops responded by singing English carols. Greetings and gifts were exchanged. They gave proper burial to their dead and both sides mourned together. They played soccer. In many sectors, this truce lasted until Christmas Day and in some areas it lasted until New Year's Day. There would be other informal treaties during that war, but none of the same size.

A Carol from Flanders
by Frederick Niven

In Flanders on the Christmas morn
The trenched foemen lay,
the German and the Briton born,
And it was Christmas Day.

The red sun rose on fields accurst,
The gray fog fled away;
But neither cared to fire the first,
For it was Christmas Day!

They called from each to each across
The hideous disarray,
For terrible has been their loss:
"Oh, this is Christmas Day!"

Their rifles all they set aside,
One impulse to obey;
'Twas just the men on either side,
Just men — and Christmas Day.

They dug the graves for all their dead
And over them did pray:
And Englishmen and Germans said:
"How strange a Christmas Day!"

Between the trenches then they met,
Shook hands, and e'en did play
At games on which their hearts were set
On happy Christmas Day.

Not all the emperors and kings,
Financiers and they
Who rule us could prevent these things —
For it was Christmas Day.

Oh ye who read this truthful rime
From Flanders, kneel and say:
God speed the time when every day
Shall be as Christmas Day.