| 22 April 1073 | Rome [administration] | Following the death of Alexander II, Deacon Hildebrand, a radical church reformer, is elected by popular acclaim as Pope Gregory VII. |
| 22 April 1164 | Papal States, Italy, Holy Roman Empire [administration] | Guido of Crema is (uncanonically) elected Pope Paschal III in succession to the late antipope Victor IV. The Holy Roman Emperor Frederick I Barbarossa gives him protection, but German prelates who had recognized Victor as pope refuse to accept Paschal. |
| 22 April 1451 | Castile [births and deaths] | Isabella I the Catholic, Queen of Castile 1474–1504 and Aragon 1479–1504, who ruled the two kingdoms jointly with her husband, Ferdinand, from 1479, born in Madrigal de las Altas Torres, Castile (–1504). |
| 22 April 1529 | Spain, Portugal, Pacific [treaties] | Against the opposition of the Spanish Cortes (parliament), the Holy Roman Emperor Charles V, who is also King Charles I of Spain, signs the Treaty of Zaragoza with King John III of Portugal, dividing the Pacific into respective spheres of influence; for 350,000 ducats Spain is to leave the Moluccas and any territories up to 15 degrees east of them. |
| 22 April 1616 | Spain [births and deaths] | Miguel de Cervantes Saavedra, celebrated Spanish novelist, dramatist and poet, whose best-known work is Don Quixote (1605, 1615), dies in Madrid, Spain (68). |
| 22 April 1724 | Prussia [births and deaths] | Immanuel Kant, German philosopher whose work had a major influence on subsequent philosophy, born in Königsberg, Prussia (–1804). |
| 22 April 1870 | Russia, USSR [births and deaths] | Vladimir Ilyich Lenin, founder of the Russian Communist Party, leader of the Russian Revolution, and head of the Soviet Union 1917–24, born in Simbirsk, Russia (–1924). |
| 22 April 1904 | [births and deaths] | J Robert Oppenheimer, US theoretical physicist and director of the Los Alamos laboratory which built the first atomic bomb, born in New York City (–1967). |
| 22 April–25 May 1915 | Belgium [World War I (1914–18)] | At the Second Battle of Ypres, Belgium, a German counteroffensive pushes the Western Front in southwestern Belgium forward by 5 km/3 mi. |
| 22 April–17 June 1954 | USA [human rights] | The McCarthy ‘witch-hunts’ reach their peak as Wisconsin senator Joseph McCarthy, chairman of the Senate Permanent Investigations Subcommittee, alleges that a communist spy ring is active at the US Army Signal Corps headquarters at Fort Monmouth, New Jersey. During the hearings, which are televised across the country, McCarthy accuses the Army secretary of deliberately concealing evidence. McCarthy's conduct turns public opinion against him. |
| 22 April 1970 | USA, world [conservation] | Millions of Americans participate in the first ‘Earth Day’ as a series of mass meetings, speeches, and events take place across the USA. |
| 22 April 1994 | USA [births and deaths] | Richard M(ilhous) Nixon, 37th president of the USA 1969–74, a Republican, the first president to resign, dies in New York City (81). |
| 22 April 1997 | Peru [terrorism] | Troops storm the Japanese ambassador's residence in Lima, Peru, ending the hostage crisis which began on 17 December 1996; all 14 Tupac Amarú guerrillas are killed. |
| 22 April 1998 | England [health and medicine] | Scientists at the Public Health Laboratory Service in London, England, report the discovery of a bacterium Pseudonas aeruginosa that is resistant to all known antibiotics. It causes a wide range of infections in people with impaired immune systems. |
| 22 April 1998 | UK [women's rights] | The UK army introduces ‘gender-free’ physical recruitment tests to give women a better chance of entering the armed forces. |
