THIS DAY IN HISTORY ― MAY 21

May 21 is the 141st day of the year (142nd in leap years) in the Gregorian calendar. There are 224 days remaining until the end of the year. 

NATIONAL MEMO DAY 

1659 – In the Concert of The Hague, the Dutch Republic, the Commonwealth of England and the Kingdom of France set out their views on how the Second Northern War should end.

1725 – The Order of St. Alexander Nevsky is instituted in Russia by Empress Catherine I. It would later be discontinued and then reinstated by the Soviet government in 1942 as the Order of Alexander Nevsky. 

1851 – Slavery is abolished in Colombia, South America.

1863 – American Civil War: The Union Army succeeds in closing off the last escape route from Port Hudson, Louisiana, in preparation for the coming siege.

1864 – Russia declares an end to the Russo-Circassian War and many Circassians are forced into exile. The day is designated the Circassian Day of Mourning.

1864 – American Civil War: The Battle of Spotsylvania Court House ends. It was the second major battle in Lt. Gen. Ulysses S. Grant's 1864 Overland Campaign.

1871 – French troops invade the Paris Commune and engage its residents in street fighting. By the close of "Bloody Week", some 20,000 communards have been killed and 38,000 arrested.

1881 – The American Red Cross is established by Clara Barton in Washington, D.C.

1911 – President of Mexico Porfirio Díaz and the revolutionary Francisco Madero sign the Treaty of Ciudad Juárez to put an end to the fighting between the forces of both men, concluding the initial phase of the Mexican Revolution.

1917 – The Great Atlanta fire of 1917 causes $5.5 million in damages, destroying some 300 acres including 2,000 homes, businesses and churches, displacing about 10,000 people but leading to only one fatality (due to heart attack).

1927 – Aviator Charles A. Lindbergh touches down at Le Bourget Field in Paris, completing the world's first solo nonstop flight across the Atlantic Ocean.

1932 – Bad weather forces aviator Amelia Earhart to land in a pasture in Derry, Northern Ireland, but she thereby becomes the first woman to fly solo across the Atlantic Ocean.

1946 – Physicist Louis Slotin is fatally irradiated in a criticality incident during an experiment with the demon core at Los Alamos National Laboratory.

1972 – Michelangelo's Pietà in St. Peter's Basilica in Rome is damaged by a vandal, the mentally disturbed Hungarian geologist Laszlo Toth.

1991 – Former Indian Prime Minister Rajiv Gandhi is assassinated by a female suicide bomber near Madras.

1992 – After 30 seasons Johnny Carson hosted his penultimate episode of The Tonight Show, featuring guests (Robin Williams and Bette Midler).

1996 – The ferry MV Bukoba sinks in Tanzanian waters on Lake Victoria, killing nearly 1,000.
2001 – French Taubira law is enacted, officially recognizing the Atlantic slave trade and slavery as crimes against humanity.

2014 – The National September 11 Museum opens to the public.

BORN TODAY 

1688 – Alexander Pope, English poet, essayist, and translator (d. 1744)

1844 – Henri Rousseau, French painter (d. 1910)

1898 – Armand Hammer, American physician and businessman, founded Occidental Petroleum (d. 1990)

1921 – Andrei Sakharov, Russian physicist and academic, Nobel Prize laureate (d. 1989)

1947 – Linda Laubenstein, American physician and academic (d. 1992)

From Wikipedia and Google (images), ex as noted.