· 1506 – Christopher Columbus dies, Italian explorer, discovered the Americas (b. 1451)
· 1862 – U.S. President Abraham Lincoln signs the Homestead Act into law.
· 1873 – Levi Strauss and Jacob Davis receive a U.S. patent for blue jeans with copper rivets.
· 1883 – Krakatoa begins to erupt; the volcano explodes three months later, killing more than 36,000 people.
· 1899 – The first traffic ticket in the US: New York City taxi driver Jacob German was arrested for speeding while driving 12 miles per hour on Lexington Street.
· 1902 – Cuba gains independence from the United States. Tomás Estrada Palma becomes the country's first President.
· 1940 – Holocaust: The first prisoners arrive at a new concentration camp at Auschwitz
· 1956 – In Operation Redwing (shot Cherokee), the first United States airborne hydrogen bomb is dropped over Bikini Atoll in the Pacific Ocean.
· 1983 – First publications of the discovery of the HIV virus that causes AIDS in the journal Science by Luc Montagnier.
· 1989 – The Chinese authorities declare martial law in the face of pro-democracy demonstrations, setting the scene for the Tiananmen Square massacre.
Facts from http://en.wikipedia.org/wiki/May_20