* 238 – Gordian II lost the Battle of Carthage against the Numidian forces loyal to Maximinus Thrax and is killed. Gordian I, his father, commits suicide.
* 467 – Anthemius is elevated to Emperor of the Western Roman Empire.
* 1204 – The Crusaders of the Fourth Crusade breach the walls of Constantinople and enter the city, which they completely occupy the following day.
* 1557 – Cuenca is founded in Ecuador.
* 1606 – The Union Flag is adopted as the flag of Great Britain.
* 1633 – The formal inquest of Galileo Galilei by the Inquisition begins.
* 1776 – American Revolution: With the Halifax Resolves, the North Carolina Provincial Congress authorizes its Congressional delegation to vote for independence from Britain.
* 1820 – Alexander Ypsilantis is declared leader of Filiki Eteria, a secret organization to overthrow Ottoman rule over Greece.
* 1831 – Soldiers marching on the Broughton Suspension Bridge in Manchester, England cause it to collapse.
* 1861 – American Civil War: The war begins with Confederate forces firing on Fort Sumter, in the harbor of Charleston, South Carolina.
* 1862 – American Civil War: The Andrews Raid (the Great Locomotive Chase) occurred, starting from Big Shanty, Georgia (now Kennesaw).
* 1864 – American Civil War: The Fort Pillow massacre: Confederate forces kill most of the African American soldiers that surrendered at Fort Pillow, Tennessee.
* 1865 – American Civil War: Mobile, Alabama, falls to the Union Army.
* 1877 – The United Kingdom annexes the Transvaal.
* 1910 – The SMS Zrinyi, one of the last pre-dreadnoughts built by the Austro-Hungarian Navy, is launched.
* 1917 – World War I: Canadian forces successfully complete the taking of Vimy Ridge from the Germans.
* 1927 – April 12 Incident: Chiang Kai-shek orders the Communist Party of China members executed in Shanghai, ending the First United Front.
* 1934 – The strongest surface wind gust in the world at 231 mph, is measured on the summit of Mount Washington, New Hampshire.
* 1934 – The U.S. Auto-Lite Strike begins, culminating in a five-day melee between Ohio National Guard troops and 6,000 strikers and picketers.
* 1935 – First flight of the Bristol Blenheim.
* 1937 – Sir Frank Whittle ground-tests the first jet engine designed to power an aircraft, at Rugby, England.
* 1945 – U.S. President Franklin D. Roosevelt dies while in office; vice-president Harry Truman is sworn in as the 33rd President.
* 1954 – Bill Haley & His Comets record "Rock Around the Clock" in New York City.
* 1955 – The polio vaccine, developed by Dr. Jonas Salk, is declared safe and effective.
* 1961 – The Russian (Soviet) cosmonaut Yuri Gagarin becomes the first human to travel into outer space and perform the first manned orbital flight, in Vostok 3KA-2 (Vostok 1).
The first human spaceflight is accomplished on April 12, 1961 by Soviet cosmonaut Yuri Gagarin.
* 1963 – The Soviet nuclear powered submarine K-33 collides with the Finnish merchant vessel M/S Finnclipper in the Danish straits.
* 1968 – Nerve gas accident at Skull Valley, Utah.
* 1970 – Soviet submarine K-8, carrying four nuclear torpedoes, sinks in the Bay of Biscay four days after a fire on board.
* 1980 – Samuel Doe takes control of Liberia in a coup d'état, ending over 130 years of minority Americo-Liberian rule over the country.
* 1980 – Terry Fox begins his "Marathon of Hope" at St. John's, Newfoundland.
* 1981 – The first launch of a Space Shuttle (Columbia) launches on the STS-1 mission.
* 1990 – Jim Gary's "Twentieth Century Dinosaurs" exhibition opens at the Smithsonian Institution National Museum of Natural History in Washington, D.C.
* 1992 – The Euro Disney Resort officially opens with its theme park Euro Disneyland. The resort and its park's name are subsequently changed to Disneyland Paris.
* 1994 – Canter & Siegel post the first commercial mass Usenet spam.
* 1998 – An earthquake in Slovenia, measuring 5.6 on the Richter scale occurs near the town of Bovec.
* 1999 – US President Bill Clinton is cited for contempt of court for giving "intentionally false statements" in a sexual harassment civil lawsuit.
* 2002 – A female suicide bomber detonated at the entrance to Jerusalem's Mahane Yehuda open-air market, killing 7 and wounding 104.
* 2007 – A suicide bomber penetrated the Green Zone and detonated in a cafeteria within a parliament building, killing Iraqi MP Mohammed Awad and wounding more than twenty other people.
* 2009 – Zimbabwe officially abandons the Zimbabwe Dollar as their official currency.
* 2010 – A train derails near Merano, Italy, after running into a landslide, causing nine deaths and injuring 28 people.