From the Fold3 Blog:
On November 11, 1921, President Warren G. Harding presided over the dedication of the Tomb of the Unknown Soldier at Arlington National Cemetery in Washington, D.C. The monument honored fallen U.S. servicemen from WWI whose remains were unidentified. The ceremony took place the same day the country was celebrating the newly declared Armistice Day holiday.
Construction begins on the Tomb of the Unknown Soldier, 1921
During WWI, the chaos of battle resulted in scores of unidentified dead servicemen. The creation of the memorial, also known as the Tomb of the Unknowns, was proposed in 1920 by New York Congressman and WWI veteran Hamilton Fish. Both Great Britain and France had dedicated similar monuments in 1920, and in March 1921, Congress approved the plan to build America’s tribute to unidentified fallen soldiers.
You can read a lot more at: https://blog.fold3.com/100th-anniversary-of-the-tomb-of-the-unknown-soldier-november-11-2021/