“Veterans Day, formerly known as Armistice Day, was originally set as a U.S. legal holiday to honor the end of World War I, which officially took place on November 11, 1918. In 1938, through an act of Congress, November 11th was made a legal holiday.”
https://www.govinfo.gov/features/veterans-day
Learn more:
https://www.va.gov/opa/vetsday/vetdayhistory.asp