| 1 May 1045 | Italy, Holy Roman Empire [political events] | Pope Benedict IX resigns, after selling the papal office to John Gratian, who is elected as Gregory VI. |
| 1 May 1278 | Byzantine Empire, Greece [administration] | William de Villehardouin, Prince of Achaea, dies. He is succeeded by Charles of Anjou, King of Sicily. Although apparently threatening the Byzantine Empire, Achaea is exhausted by war and the Byzantine Empire is able to extend its territories as far as Arcadia. |
| 1 May 1308 | Holy Roman Empire, Germany [political events] | The Holy Roman Emperor Albert I is murdered by John, Duke of Swabia. |
| 1 May 1355 | Genoa, Venice, Italy [diplomacy] | Genoa and Venice make peace. |
| 1 May 1625 | UK, France [political events] | King Charles I of Great Britain and Ireland marries Henrietta Maria, sister of King Louis XIII of France, by proxy; George Villiers, Duke of Buckingham, stands in for the king at the ceremony in Paris, France. |
| 1 May 1700 | England [births and deaths] | John Dryden, outstanding English poet, playwright, and critic, poet laureate, whose major works include ‘Annus Mirabilis’ (1667) and Marriage à la mode (1672), dies (68). |
| 1 May 1707 | UK [political events] | The Act of Union unites England and Scotland as the United Kingdom of Great Britain. The terms of the act provide for: (a) the Hanoverian succession; (b) one Parliament, to which Scotland is to send members; (c) the churches remaining as before; and (d) adoption of one flag, the Union Jack. |
| 1 May 1756 | France, Austria [treaties] | The Treaty of Versailles between France and Austria constitutes the Diplomatic Revolution, achieved by the Austrian chancellor Prince Kaunitz-Rietberg. The Habsburg Monarchy is to be neutral in an Anglo-French war but either party is to aid the other if attacked by Prussia. In addition, France is to recognize the Austrian Netherlands and to aid Austria if the latter is attacked by the Ottoman Empire. |
| 1 May 1757 | France, Holy Roman Empire, Prussia, Silesia, Germany, Austrian Netherlands, Spain, Parma, Italy, Habsburg Monarchy [Seven Years War (1754–62)] | The second Treaty of Versailles against Prussia is negotiated between France and the Holy Roman Empire, by which Prussia is to be partitioned, losing Silesia and Glatz to Austria. King Louis XV of France agrees to increase annual subsidies to Maria Theresa of Austria until she has recovered Silesia. In return, she promises Louis XV full sovereignty in some cities in the Austrian Netherlands; the remainder are to pass to Don Philip, Farnesan prince of Spain, in exchange for the Italian duchies of Parma, Piacenza, and Guastalla, when these are returned to Austria. |
| 1 May 1769 | Ireland [births and deaths] | Arthur Wellesley (later Duke of Wellington), British army commander and Tory prime minister 1828–30, born in Dublin, Ireland (–1852). |
| 1 May 1840 | UK [everyday life] | The world's first postage stamp, the Penny Black, is issued in Britain, the first adhesive stamp to be used commercially. |
| 1 May–18 September 1851 | UK [buildings] | The Great Exhibition is held in Hyde Park, London, England. Devised by Prince Albert, it is the first exhibition to display the latest technical innovations in industry, from both Britain and Europe. Exhibits are housed in the Crystal Palace, a large iron and glass structure, designed by English architect Joseph Paxton. |
| 1 May 1873 | Zambia [births and deaths] | David Livingstone, Scottish missionary and explorer who explored much of East Africa in search of the source of the River Nile, dies in Chitambo, Barotseland (Zambia) (59). |
| 1 May 1883 | Germany [welfare] | Chancellor Otto von Bismarck introduces a state sickness insurance scheme in Germany to lessen the appeal of socialism to the working classes. |
| 1 May 1896 | Persia [law and government] | The Shah of Persia Nasir ud-Din is murdered and is succeeded by his son Muzaffar ud-Din. |
| 1 May 1923 | [births and deaths] | Joseph Heller, US novelist known best for Catch 22 (1961), born in Brooklyn, New York City. |
| 1 May 1925 | Cyprus, UK [colonies and mandate] | Cyprus is declared a British crown colony (having been occupied in 1914). |
| 1 May–3 November 1943 | USA [unions and associations] | A lengthy coal-miners' strike takes place in the USA. |
| 1 May 1960 | USSR, USA [crime and punishment] | Soviet military forces shoot down a US high-altitude U-2 spy aircraft over the Ural Mountains, USSR. On 19 August, the pilot Gary Powers is sentenced to ten years of imprisonment for espionage. |
| 1–4 May 1970 | USA [wars] | Demonstrations begin at universities across the USA in protest at military intervention in Cambodia; the National Guard fire on a peaceful demonstration at Kent State University, Ohio, killing four students. |
| 1 May 1972 | South Vietnam, North Vietnam [Vietnam War (1954–75)] | The South Vietnamese city of Quang Tri falls to North Vietnamese forces. |
| 1 May 1978 | UK [fairs and festivals] | The UK celebrates May Day as a public holiday for the first time. |
| 1 May 1994 | Italy [births and deaths] | Ayrton Senna, Brazilian racing car driver, is killed at Imola, Italy, when his car crashes during the San Marino Grand Prix (34). |
| 1 May 1997 | UK [elections] | The Labour Party led by Tony Blair wins the general election in Britain; Labour wins 418 seats, the Conservatives 165, and the Liberal Democrats 46; the following day John Major resigns as leader of the Conservative Party. |
| 1 May 2004 | [international organizations] | The European Union (EU) expands to cover 450 million citizens as eight central European states – the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia, and Slovenia – together with Cyprus and Malta, become full members of the organization. The enlargement from 15 to 25 countries is the biggest in EU history. |
