| 18 May 1048 | Persia [births and deaths] | Omar Khayyam, Persian poet, mathematician, and astronomer, famous for his Rubaiyat, born in Nishapur, Persia (–1131). |
| 18 May 1302 | Flanders, France [political events] | The French garrison is massacred in the ‘Matins of Bruges’, beginning the revolt of the Flemings against French occupation. The whole of Western Flanders is soon up in arms, and the French royal army is sent in to crush the rebels. |
| 18 May 1412 | England, France, Burgundy, Holy Roman Empire [treaties] | By the Treaty of Eltham, King Henry IV of England makes an alliance with the ‘Armagnacs’ (supporters of the late Louis, Duke of Orléans) against the duchy of Burgundy, France. |
| 18 May 1848 | Germany, Saxony [law and government] | A National Assembly composed of liberal delegates elected from all over Germany meets in Frankfurt and suspends the German Confederation prior to discussing a more unified organization of the German states. |
| 18 May 1868 | Russia [births and deaths] | Nicholas II, Tsar of Russia 1895–1917, born in Tsarskoye Selo, near St Petersburg, Russia (–1918). |
| 18 May 1896 | USA [law and government] | The US Supreme Court, in Plessy v. Ferguson, upholds the concept of separate railway cars for black Americans, creating the basis for segregationist provision of ‘separate but equal’ public facilities in the USA, known as Jim Crow. |
| 18 May 1897 | Italy, USA [births and deaths] | Frank Capra, Italian-born US film director who directs It's a Wonderful Life and Mr Smith Goes to Washington, born near Palermo, Sicily (–1991). |
| 18 May 1917 | Russian Empire [law and government] | Prince George Lvov reforms the cabinet of the Russian provisional government with representation by socialists, and Alexander Kerensky becomes minister of war. |
| 18 May 1920 | [births and deaths] | John Paul II, pope from 1978, the first non-Italian pope in 456 years, born in Wadowice, Poland. |
| 18 May 1974 | India [political events] | An atomic bomb test makes India the world's sixth nuclear power. |
| 18 May 1978 | Italy [health and medicine] | Despite intense Vatican opposition, Italy votes to make abortion legal in the first 90 days of pregnancy. |
| 18 May 1980 | USA [natural disasters] | Mount St Helens volcano in Washington state, USA, erupts explosively in a blast 500 times more powerful than the Hiroshima bomb, causing an outbreak of fires, mudslides, and floods; 57 people die in the largest eruption in US history. Ash from the volcano blankets the surrounding area and effects global temperature readings for months to come. |
| 18–26 May 1991 | England [space exploration] | English chemist Helen Sharman becomes the first Briton to go into space, as a participant in a Soviet space mission launched in Soyuz TM-12. She spends six days with Soviet cosmonauts aboard the Mir space station. |
| 18 May 1993 | Denmark, Europe [treaties] | In a second referendum, Denmark approves the Maastricht Treaty on European union by a narrow majority, following the granting of concessions on its implementation. |
