|Holiday name||Holiday location||Holiday type|
|Senior Citizens Day||United States||Observance|
|Gospel Day (Kosrae)||Micronesia||Local Holiday|
|National Brazilian Blowout Day||-||Unofficial (Lifestyle)|
|National Spumoni Day||-||Unofficial (Food & Drinks)|
|National Senior Citizens Day||-||Unofficial (Appreciation & Honor, Awareness & Cause)|
|Ninoy Aquino Day||Philippines||Special Non-working Holiday|
|Youth Day||Morocco||National Holiday|
Historical Events on August 21
- 1331: Stefan Dušan becomes King of Serbia after defeating his father, King Stefan Uroš III.
- 1415: Portuguese forces are victorous over the Marinids after Henry the Navigator leads them to a victory at the Battle of Ceuta.
- 1680: The Spanish lose Santa Fe to the Pubeblo Indians during the Pueblo Revolt.
- 1770: Eastern Australia is claimed by James Cook who names it New South Wales.
- 1778: British forces attack the French outpost at Pondichéry during the American Revolutionary War.
- 1791: A voodoo ceremony presided over by Dutty Boukman devolves into a slave rebellion which sparks the Haitian Revolution.
- 1852: Fort Selkirk in the Yukon Territory is destroyed by Tlingit Indians.
- 1863: Pro-Confederate guerrillas known as Quantrill’s Raiders destroy the town of Lawrence, Kansas.
- 1888: William Seward Burroughs patents his adding machine in the United States.
- 1897: American automaker Oldsmobile is founded.
- 1911: A Louvre employee steals one of the most famous paintings in the world, the Mona Lisa.
- 1914: The Germans successfully attack across the Sambre River during the Battle of Chaleroi during World War I.
- 1918: During World War I, the Second Battle of Somme starts.
- 1942: American forces defeat an attack by Japanese force in the Battle of the Tenaru during World War II.
- 1942: The Nazi flag of Germany is raised on top of the highest peak in the Caucasus Mountain Range: Mount Elbrus.
- 1944: Polish and Canadian forces capture the town of Falaise, Calvados, France.
Famous Birthdays on August 21
- French painter Jean-Baptiste Greuze is born in 1725.
- Scottish engineer and inventor William Murdock is born in 1754.
- German Painter Christian Schad is born in 1894.
- American marine biologist Stephen Hillenburg is born in 1961.
- King of Morocco Mohammed VI of Morocco is born in 1963.
- American baseball player Jim Bullinger is born in 1965.