May 20: Armed Forces Day in the United States ( 2006); National Day in Cameroon ( 1972), Independence Day in East Timor ( 2002)
- 325 - The First Council of Nicaea, the first ecumenical council of the Christian Church, was formally opened in present-day Iznik, Turkey.
- 1498 - Portuguese explorer Vasco da Gama (pictured) arrived at Calicut, India.
- 1570 - Cartographer Abraham Ortelius issued the first modern atlas.
- 1862 - U.S. President Abraham Lincoln signed the Homestead Act into law.
- 1927 - By the Treaty of Jedda, the United Kingdom recognized the sovereignty of King Ibn Saud in the Kingdoms of Hejaz and Nejd, which later merged to become the Kingdom of Saudi Arabia.