March 20: Purim ends at sundown (Judaism, 2011); Equinox Earth Day (2011); Nowruz in Iran, Central Asia, and Zoroastrianism (2011); Independence Day in Tunisia (1956)
- 235 – Maximinus Thrax succeeded to the throne of the Roman Empire, the first of the so-called barracks emperors who gained power by virtue of his command of the army.
- 1602 – The Dutch East India Company was established.
- 1923 – Arts Club of Chicago hosted the opening of Pablo Picasso’s first United States showing, entitled Original Drawings by Pablo Picasso, becoming an early proponent of modern art in the U.S.
- 1944 – World War II: Four thousand U.S. Marines made a landing on Emirau Island in the Bismarck Archipelago to develop an airbase as part of Operation Cartwheel.
- 1987 – The antiretroviral drug zidovudine (AZT) (chemical structure pictured) became the first antiviral medication approved for use against HIV and AIDS.