The origin of Veterans Day has roots in the first world war. In 1918, on the eleventh hour of the eleventh day in the eleventh month, the world rejoiced and celebrated the end of four years of bitter war, with the signing of an armistice. The following year, President Woodrow Wilson proclaimed November 11, 1919 as Armistice Day in the United States, to remember the sacrifices that men and women made during World War I in order to ensure a lasting peace.
Read more about how Armistice Day evolved into the Veterans Day holiday we celebrate today, honoring all who served in the armed forces. The U.S. Department of Veterans Affairs has a great article about the history of Veterans Day.