World War I officially ended on June 28, 1919, with the signing of the Treaty of Versailles. The actual fighting between the Allies and Germany, however, had ended seven months earlier with the armistice, which went into effect on the eleventh hour of the eleventh day of the eleventh month in 1918. Armistice Day, as November 11 became known, officially became a holiday in the United States in 1926, and a national holiday 12 years later. On June 1, 1954, the name was changed to Veterans Day to honor all U.S. veterans.
In 1968, new legislation changed the national commemoration of Veterans Day to the fourth Monday in October. It soon became apparent, however, that November 11 was a date of historic significance to many Americans. Therefore, in 1978 Congress returned the observance to its traditional date.
Official, national ceremonies for Veterans Day center around the Tomb of the Unknowns.
To honor these men, symbolic of all Americans who gave their lives in all wars, an Army honor guard, the 3d U.S. Infantry (The Old Guard), keeps day and night vigil.
At 11 a.m. on November 11, a combined color guard representing all military services executes "Present Arms" at the tomb. The nation's tribute to its war dead is symbolized by the laying of a presidential wreath and the playing of "Taps." (from infoplease.com)