The first World War ended on November 11, 1918. Armistice Day was observed the next year. In 1954, Armistice Day became Veterans Day.
From a letter by American Lieutenant Lloyd Brewer Palmer, November 15, 1918:
Dearest Mother:The PBS site for War Letters (an episode from the documentary series American Experience) includes a transcript with the text of this letter and many others.
November 11th 1918 will always be remembered by yours truly. We moved out at 4:00 AM in a heavy mist and marched about 4 km. At 9:30 there was a terrific German barrage. I sure thought it was all up.
At 10:45 the order came to cease firing. Rumors started to spread that it was the end and I am sure I was not the only one to utter a prayer that it was true. Then, 11 o'clock, and a dead silence! That was absolutely the happiest moment of my life.
War Letters (PBS)