The guns of the Great War finally fell silent when Germany signed an armistice with the Allied powers on Nov. 11, 1918. It took effect at the 11th hour of the 11th day of the 11th month. The agreement halted the four-year war that aligned the era's great powers against one another, killed millions of soldiers, dismantled empires and utterly devastated Europe. The following year, Armistice Day was observed for the first time in the U.S. In 1921, the first burial of an unknown soldier took place at Arlington National Cemetery, and by 1938, the day had become an official national holiday. It was later changed to Veterans Day in 1954 in honor of soldiers from all wars.