| 20 May 1217 | England, France [wars] | William the Marshal, leading the loyalists for King Henry III of England, defeats the French dauphin Louis and the rebels who invited him to become king at Lincoln, England. |
| 20 May 1303 | France, England [treaties] | King Philip IV of France and King Edward I of England make peace in the Treaty of Paris, in which the French duchy of Gascony is restored to Edward for which he must pay fealty to Philip. |
| 20 May 1498 | India, Portugal [exploration] | The Portuguese expedition under Vasco da Gama reaches the port of Calicut on the southwest coast of India where it is welcomed by Zamorin, the Hindu ruler, as the first European expedition to sail to India since the Romans. |
| 20 May 1648 | Poland [births and deaths] | Wladyslaw IV Vasa, king of Poland 1632–48, who secured Poland against the Russians and Turks, dies in Merecz, Poland (52). |
| 20 May 1795 | France [French Revolution] | On ‘Prairial 1’ of the revolutionary calendar, popular unrest again threatens the National Convention in Paris, France, leading to the ‘White Terror’ purge of extreme revolutionaries and the end of Montagnard influence in the Convention. |
| 20 May 1799 | France [births and deaths] | Honoré de Balzac, French novelist whose writings helped establish the modern form of the novel, born in Tours, France (–1850). |
| 20 May 1834 | France [births and deaths] | Marie-Joseph-Paul-Yves-Roch-Gilbert de Motier, marquis de Lafayette, French aristocrat and political leader who fought against the British during the American Revolution, dies in Paris, France (76). |
| 20 May 1875 | France [weights and measures] | The International Bureau of Weights and Measures is established in France by a treaty signed in Paris. Located at Sèvres, its purpose is to unify systems of measurement, and to establish standards by providing a prototype metre and kilogram as the basis for all scientific and other measures. |
| 20 May 1882 | Italy, Austria-Hungary, Germany [treaties] | Italy joins the Austro-German alliance for a period of five years, thereby forming the Triple Alliance (which is subsequently renewed until 1915). This assures Italy of support in the event of attack by France, commits Italy to support Germany in the event of a French attack on Germany, and guarantees Italian neutrality in the event of war between Austria-Hungary and Russia. |
| 20 May 1885 | Saudi Arabia, Iraq [births and deaths] | Faisal I, King of Iraq 1921–33 and promoter of pan-Arab nationalism, born in Mecca, Hejaz (–1933). |
| 20 May 1908 | [births and deaths] | James Stewart, US actor, born in Indiana, Pennsylvania (–1997). |
| 20–22 May 1913 | United Kingdom [gardens] | The Royal Horticultural Society holds the first Chelsea Flower Show, in London, England. |
| 20 May 1920 | Mexico [terrorism] | President Venustiano Carranza of Mexico is assassinated. In response the US government suspends diplomatic relations with Mexico. Adolfo de la Huerta takes office as provisional president of Mexico. |
| 20–21 May 1927 | USA [aircraft] | US aviator Charles Lindbergh, in his single-engine aircraft Spirit of St Louis, flies from New York City to Paris, France, the first nonstop solo transatlantic flight. He arrives at Le Bourget Airfield, outside Paris, France, at 10:24 p.m., 33 hr 29 min after departing Roosevelt Field, Long Island, New York. |
| 20–21 May 1932 | [aircraft] | US aviator Amelia Earhart flies from Newfoundland, Canada, to Londonderry, Northern Ireland, in 13.5 hours, the first woman to make a solo flight across the Atlantic. |
| 20 May 1941 | USA [legislation] | President Roosevelt moves Thanksgiving to the last Thursday of November, ending a two-year experiment in which it was the fourth Thursday of the month. |
| 20 May 1988 | UK [food and drink] | The Licensing Act in Britain allows all-day opening (from 11 am to 11 pm) to pubs in England and Wales. |
| 20 May 2002 | East Timor [political events] | East Timor achieves formal independence from Indonesia and becomes a nation state under the recently-elected president Xanana Gusmão, the former guerrilla leader of the Revolutionary Front for an Independent East Timor (FRETELIN). Indonesia's claim to sovereignty after its military occupation in 1975 was never recognized by the United Nations, which has administered the territory since 1999 when the East Timorese voted for secession in a referendum despite violent intimidation by pro-Indonesian militias. |
| 20 May 2005 | UK [physiology] | Scientists at Newcastle University report that they have successfully cloned a human embryo as part of their stem cell research into new treatments for diabetes, having been granted a licence by the UK Human Fertilisation and Embryology Authority in August 2004. Pro-life groups criticize such work as unethical. |
