May 31: World No Tobacco Day; Feast of the Visitation in Roman Catholicism and Anglicanism
- 1279 BC – According to estimates accepted by most Egyptologists today, Ramesses II became Pharaoh of Egypt.
- 1223 – Mongol invasions: Mongol forces defeated a combined army of Kiev, Galich, and the Cumans on the banks of the Kalchik River in present-day Ukraine.
- 1862 – American Civil War: Confederate forces under Joseph E. Johnston and G. W. Smith engaged Union forces under George B. McClellan at the Battle of Seven Pines outside Richmond, Virginia.
- 1981 – An organized mob of police and government-sponsored paramilitias began burning the public library in Jaffna, Sri Lanka, destroying over 97,000 items in one of the most violent examples of ethnic biblioclasm of the 20th century.
- 2010 – During an attempt to break the ongoing blockade of the Gaza Strip, the Israeli Navy engaged in armed conflict with the crew of the MV Mavi Marmara (pictured), resulting in nine civilian deaths.