| 12 April 1111 | Holy Roman Empire, Papal States, Italy [political events] | Emperor Henry V of Germany forces Pope Paschal II to concede to him the right to invest bishops by threatening to recognize the antipope Sylvester IV. Henry then orders Sylvester to abdicate. |
| 12 April 1204 | Byzantine Empire [Crusades (1095–1272)] | Realizing that the Byzantine promise of help for their crusade is not going to be kept, the crusaders take the Byzantine capital Constantinople by storm and sack it for three days. The emperor Alexius V Ducas Murtzuphlus flees, as does Constantine XI Lascaris after being offered the throne by Byzantine nobles during the attack. |
| 12 April 1844 | USA, Republic of Texas [treaties] | The US and the Republic of Texas sign the Texas Annexation Treaty, making Texas a US territory. |
| 12–13 April 1861 | USA [American Civil War (1861–65)] | Confederate forces take the federal garrison of Fort Sumter, Charleston, South Carolina, after a 40-hour bombardment, marking the outbreak of the American Civil War. |
| 12 April 1877 | UK, Transvaal [colonization] | The British colonial administrator Theophilus Shepstone annexes the southern African Republic of Transvaal for Britain on grounds of bankruptcy and danger from Basutos and Zulus, though this annexation violates the Sand River Convention of 1852. |
| 12 April 1937 | England [technology] | English engineer Frank Whittle tests the first prototype jet engine. A similar engine is developed in Germany at the same time. |
| 12 April 1945 | USA [births and deaths] | Franklin Delano Roosevelt, US statesman, 32nd president of the USA 1933–45 (re-elected three times), a Democrat, dies in Warm Springs, Georgia (63). |
| 12 April 1945 | USA [political events] | Following the death of Franklin Delano Roosevelt, president of the USA, he is succeeded by Vice-President Harry S Truman. |
| 12–14 April 1981 | USA [aircraft] | The US reusable space shuttle, using the orbiter Columbia, makes its first flight (second shuttle flight 12–14 November). It is also the first landing of a US spacecraft on land. |
| 12 April 1981 | USA [births and deaths] | Joe Louis, US world heavyweight champion boxer 1937–49, dies in Las Vegas, Nevada (66). |
| 12 April 1992 | France [everyday life] | The theme park EuroDisney (later Disneyland Paris) opens at Marne-la-Vallée, just outside Paris, France. Development has cost $4.5 billion. |
| 12 April 1998 | USA [statistics and demography] | The US Census Bureau reports that 26 million Americans, nearly one in ten, is an immigrant. Most come from Central or South America. |
| 12 April 1999 | Federal Republic of Yugoslavia [Balkan conflicts (c. 1991–2000)] | Foreign ministers from NATO's 19 member countries meet for the first time since bombing began in Kosovo. They pledge to continue the bombing campaign until Yugoslav president Slobodan Miloševic withdraws his forces from Kosovo and allows ethnic Albanian refugees to return safely. |
| 12 April 2005 | UK [business and economics] | The supermarket group Tesco, with a 30% share of the British grocery market, becomes the first UK retail store chain to announce annual profits of more than £2 billion. |
