1775: The Siege of Boston begins during the American Revolutionary War.
1792: France declares war on Austria, marking the start of the French Revolutionary Wars.
1836: The U.S. Congress passes an act creating the Wisconsin Territory.
1861: Robert E. Lee resigns from the United States Army two days after he was offered command of the Union Army and three days after Virginia seceded from the Union.
1889: Adolf Hitler, the dictator of Nazi Germany, was born in Braunau am Inn, Austria.
1902: Pierre and Marie Curie isolated radium.
1906: The 1906 Summer Olympics opened in Athens, Greece, the first modern Olympic Games.
1914: The Ludlow Massacre occurred in Colorado, USA, during a coal miners' strike.
1918: Manfred von Richthofen, also known as the Red Baron, was shot down and killed in World War I.
1940: The British War Cabinet approved the Gallipoli Campaign during World War II.
1945: During World War II, U.S. troops capture Leipzig, Germany, near the end of the war in Europe.
1968: English politician Enoch Powell delivers his controversial "Rivers of Blood" speech regarding immigration and anti-discrimination legislation.
1972: Apollo 16 astronauts John Young and Charles Duke explore the Moon's Descartes Highlands.
1986: Michael Jordan sets an NBA playoff record by scoring 63 points in a game against the Boston Celtics.
1999: The Columbine High School massacre occurs in Colorado, USA, resulting in the deaths of 13 victims and the perpetrators.
2008: Danica Patrick wins the Indy Japan 300, becoming the first female driver to win an IndyCar Series race.
2010: An explosion on the Deepwater Horizon oil rig in the Gulf of Mexico leads to one of the largest oil spills in history.
2013: A series of bombings in Iraq, including a car bomb attack in Baghdad, kills dozens of people and injures many more.
2018: Former U.S. President George H.W. Bush is hospitalized a day after his wife Barbara Bush's funeral, suffering from a blood infection.
2021: NASA's Mars helicopter, Ingenuity, makes its first powered flight on another planet, marking a milestone in space exploration.