In 1914, during the Great War (World War I), an unofficial truce took place on Christmas Day along the Western Front. Some German and British soldiers took it upon themselves to celebrate Christmas by stopping the war, greeting each other, exchanging what small items they had as gifts (cigarettes, chocolate, etc.) and playing a soccer game. Peace broke out in more than one area and in more than one year.
There is a memorial in Ypres, Belgium commemorating this truce that was lead by the soldiers themselves.
This is my favorite Christmas story.