21 August, 1911: Leonardo da Vinci's Mona Lisa (above) was stolen from the Louvre by Vincenzo Perugia, an Italian waiter. The theft, in the middle of the night, embarrassed the Louvre, which believed it would never be stolen since it was too famous to be sold. The whereabouts of the painting remained a mystery for three- and-a-half years, until it was discovered in Florence. Perugia was sentenced to one year and 15 days in prison.
1939: Civil defence started in Britain.
1940: Leon Trotsky was assassinated in Mexico on the orders of Joseph Stalin. Ramon Mercader went to his house pretending to be a supporter, and buried an ice pick in his skull.
1959: Hawaii became the 50th of the United States.
1968: Russian tanks entered Czechoslovakia to crush the Prague Spring.Reuse content