* 1323 – The University of Rome La Sapienza is instituted by Pope Boniface VIII.
* 1453 – The last naval battle in Byzantine history occurs, as three Genoese galleys escorting a Byzantine transport fight their way through the huge Ottoman blockade fleet and into the Golden Horn.
* 1526 – The last ruler of the Lodi Dynasty, Ibrahim Lodi is defeated and killed by Babur in the First Battle of Panipat.
* 1534 – Jacques Cartier begins the voyage during which he discovers Canada and Labrador.
* 1535 – The Sun dog phenomenon observed over Stockholm and depicted in the famous painting "Vädersolstavlan".
* 1653 – Oliver Cromwell dissolves the Rump Parliament.
* 1657 – Admiral Robert Blake destroys a Spanish silver fleet under heavy fire at Santa Cruz de Tenerife.
* 1657 – Freedom of religion is granted to the Jews of New Amsterdam (later New York City).
* 1689 – The former King James II of England, now deposed, lays siege to Derry.
* 1770 – The Georgian king Erekle II, abandoned by his Russian ally Count Totleben, wins a victory over Ottoman forces at Aspindza.
* 1775 – American Revolutionary War: the Siege of Boston begins, following the battles at Lexington and Concord.
* 1792 – France declares war on Austria, the beginning of French Revolutionary Wars.
* 1809 – Two Austrian army corps in Bavaria are defeated by a First French Empire army led by Napoleon I of France at the Battle of Abensberg on the second day of a four day campaign that ended in a French victory.
* 1810 – The Governor of Caracas declares independence from Spain.
* 1818 – The case of Ashford v Thornton ends, with Abraham Thornton allowed to go free rather than face a retrial for murder, after his demand for trial by battle is upheld.
* 1828 – René Caillié becomes the first non-Muslim to enter Timbouctou.
* 1836 – U.S. Congress passes an act creating the Wisconsin Territory.
* 1861 – American Civil War: Robert E. Lee resigns his commission in the United States Army in order to command the forces of the state of Virginia.
* 1862 – Louis Pasteur and Claude Bernard complete the first pasteurization tests.
* 1865 – Astronomer Pietro Angelo Secchi demonstrates the Secchi disk, which measures water clarity, aboard Pope Pius IX's yacht, the L’Immaculata Concezion.
* 1871 – The Civil Rights Act of 1871 becomes law.
* 1876 – The April Uprising, a key point in modern Bulgarian history, leading to the Russo-Turkish War and the liberation of Bulgaria from domination as an independent part of the Ottoman Empire.
* 1884 – Pope Leo XIII publishes the encyclical Humanum Genus.
* 1902 – Pierre and Marie Curie refine radium chloride.
* 1908 – Opening day of competition in the New South Wales Rugby League.
* 1912 – Opening day for baseball's Tiger Stadium in Detroit, Michigan, and Fenway Park in Boston, Massachusetts.
* 1914 – 19 men, women, and children die in the Ludlow Massacre during a Colorado coal-miner's strike.
* 1916 – The Chicago Cubs play their first game at Weeghman Park (currently Wrigley Field), defeating the Cincinnati Reds 7-6 in 11 innings.
* 1918 – Manfred von Richthofen, aka The Red Baron, shoots down his 79th and 80th victims, his final victories before his death the following day.
* 1922 – The Soviet government creates South Ossetian Autonomous Oblast within Georgian SSR.
* 1926 – Western Electric and Warner Bros. announce Vitaphone, a process to add sound to film.
* 1939 – Adolf Hitler's 50th birthday is celebrated as a national holiday in Nazi Germany.
* 1939 – Billie Holiday records the first Civil Rights song "Strange Fruit".
* 1945 – World War II: US troops capture Leipzig, Germany, only to later cede the city to the Soviet Union.
* 1945 – World War II: Fuehrerbunker: Adolf Hitler makes his last trip to the surface to award Iron Crosses to boy soldiers of the Hitler Youth.
* 1946 – The League of Nations officially dissolves, giving most of its power to the United Nations.
* 1961 – Failure of the Bay of Pigs Invasion of US-backed troops against Cuba.
* 1964 – BBC Two launches with a power cut because of the fire at Battersea Power Station.
* 1968 – English politician Enoch Powell makes his controversial Rivers of Blood speech.
* 1972 – Apollo 16, commanded by John Young, lands on the moon.
* 1978 – Korean Air Flight 902 is shot down by the Soviet Union.
* 1980 – Climax of Berber Spring in Algeria as hundreds of Berber political activists are arrested.
* 1984 – The Good Friday Massacre, an extremely violent ice hockey playoff game, is played in Montreal, Canada.
* 1985 – The ATF raids The Covenant, The Sword, and the Arm of the Lord compound in northern Arkansas.
* 1986 – Pianist Vladimir Horowitz performs in his native Russia for the first time in 61 years.
* 1998 – German terrorist group the Red Army Faction announces their dissolution after 28 years.
* 1999 – Columbine High School massacre: Eric Harris and Dylan Klebold kill 13 people and injure 24 others before committing suicide at Columbine High School in Jefferson County, Colorado.
* 2007 – Johnson Space Center Shooting: A man with a handgun barricades himself in NASA's Johnson Space Center in Houston, Texas before killing a male hostage and himself.
* 2008 – Danica Patrick wins the Indy Japan 300 becoming the first female driver in history to win an Indy car race.
* 2010 – The Deepwater Horizon oil well explodes in the Gulf of Mexico, killing twelve workers and beginning an oil spill that would last six months.