In 1921, President Harding presided over a re-burial of an unknown American serviceman who died in WWI. Since then, the Tomb of the Unknown Soldier has hosted an unidentified serviceman from WWII, Korea and Vietnam.
Historians debate whether Crispus Attucks was a free man or an escaped slave, but they generally agree upon his role in American history on March 5, 1770.
In 1976, the United States accepted a special gift from Japanese bonsai master Masaru Yamaki: a 400-year-old bonsai tree. Welcomed as a symbol of peace and friendship, the tree became a permanent addition to the National Arboretum.