* 238 – Year of the Six Emperors: The Roman Senate outlaws emperor Maximinus Thrax for his bloodthirsty proscriptions in Rome and nominates two of its members, Pupienus and Balbinus, to the throne.
* 1500 – Portuguese navigator Pedro Álvares Cabral lands in Brazil.
* 1529 – Treaty of Saragossa divides the eastern hemisphere between Spain and Portugal along a line 297.5 leagues or 17° east of the Moluccas.
* 1809 – The second day of the Battle of Eckmühl: the Austrian army is defeated by the First French Empire army led by Napoleon I of France and driven over the Danube in Regensburg.
* 1836 – Texas Revolution: A day after the Battle of San Jacinto, forces under Texas General Sam Houston capture Mexican General Antonio López de Santa Anna.
* 1863 – American Civil War: Grierson's Raid begins – troops under Union Army Colonel Benjamin Grierson attack central Mississippi.
* 1864 – The U.S. Congress passes the Coinage Act of 1864 that mandates that the inscription In God We Trust be placed on all coins minted as United States currency.
* 1876 – The first ever National League is played in Philadelphia.
* 1889 – At high noon, thousands rush to claim land in the Land Run of 1889. Within hours the cities of Oklahoma City and Guthrie are formed with populations of at least 10,000.
* 1898 – Spanish-American War: The United States Navy begins a blockade of Cuban ports and the USS Nashville captures a Spanish merchant ship.
* 1906 – The 1906 Summer Olympics, not now recognized as part of the official Olympic Games, open in Athens.
* 1912 – Tsinghua University, one of mainland China's leading universities, is founded.
* 1912 – Pravda, the "voice" of the Communist Party of the Soviet Union, begins publication in Saint Petersburg.
* 1915 – The use of poison gas in World War I escalates when chlorine gas is released as a chemical weapon in the Second Battle of Ypres.
* 1930 – The United Kingdom, Japan and the United States sign the London Naval Treaty regulating submarine warfare and limiting shipbuilding.
* 1944 – The 1st Air Commando Group using Sikorsky R-4 helicopters stage the first use of helicopters in combat with CSAR operations in the China-Burma-India theater.
* 1944 – World War II: Operation Persecution is initiated – Allied forces land in the Hollandia (currently known as Jayapura) area of New Guinea.
* 1945 – World War II: Prisoners at the Jasenovac concentration camp revolt. 520 are killed and 80 escape.
* 1945 – World War II: Führerbunker: After learning that Soviet forces have taken Eberswalde without a fight, Adolf Hitler admits defeat in his underground bunker and states that suicide is his only recourse.
* 1948 – 1948 Arab-Israeli War: Haifa, a major port of Israel, is captured from Arab forces.
* 1954 – Red Scare: Witnesses begin testifying and live television coverage of the Army-McCarthy Hearings begins.
* 1964 – The 1964-1965 New York World's Fair opens for its first season.
* 1969 – British yachtsman Sir Robin Knox-Johnston completes the first solo non-stop circumnavigation of the world.
* 1970 – The first Earth Day is celebrated.
* 1972 – Vietnam War: Increased American bombing in Vietnam prompts anti-war protests in Los Angeles, New York City, and San Francisco.
* 1983 – The German magazine Der Stern claims that the "Hitler Diaries" had been found in wreckage in East Germany; the diaries are subsequently revealed to be forgeries.
* 1992 – In an explosion in Guadalajara, Mexico, 206 people are killed, nearly 500 injured and 15,000 left homeless.
* 1993 – Version 1.0 of the Mosaic web browser is released.
* 1997 – Haouch Khemisti massacre in Algeria – 93 villagers killed.
* 1997 – The Japanese embassy hostage crisis ends in Lima, Peru.
* 1998 – Disney's Animal Kingdom opens at Walt Disney World near Orlando, Florida, United States.
* 2000 – In a pre-dawn raid, federal agents seize six-year-old Elián González from his relatives' home in Miami, Florida.
* 2000 – The Big Number Change takes place in the United Kingdom.
* 2000 – Second Battle of Elephant Pass: Tamil Tigers capture a strategic Sri Lankan Army base and hold it for 8 years.
* 2003 – Election of the fifth Caliph of Ahmadiyya Muslim Community.
* 2004 – Two fuel trains collide in Ryongchon, North Korea, killing up to 150 people.
* 2005 – Japan's Prime Minister Junichiro Koizumi apologizes for Japan's war record.
* 2006 – 243 people are injured in pro-democracy protest in Nepal after Nepali security forces open fire on protesters against King Gyanendra.
* 2008 – The United States Air Force retires the remaining F-117 Nighthawk aircraft in service.