* 193 – Septimius Severus is proclaimed Roman Emperor by the army in Illyricum (in the Balkans).
* 475 – Byzantine Emperor Basiliscus issues a circular letter (Enkyklikon) to the bishops of his empire, supporting the Monophysite christological position.
* 1241 – Battle of Liegnitz: Mongol forces defeat the Polish and German armies.
* 1388 – Despite being outnumbered 16 to 1, forces of the Old Swiss Confederacy are victorious over the Archduchy of Austria in the Battle of Näfels.
* 1413 – Henry V is crowned King of England.
* 1440 – Christopher of Bavaria is appointed King of Denmark.
* 1454 – The Treaty of Lodi is signed, establishing a balance of power among northern Italian city-states for almost 50 years.
* 1511 – St John's College, Cambridge, England, founded by Lady Margaret Beaufort, receives its charter.
* 1585 – The expedition organised by Sir Walter Raleigh departs England for Roanoke Island (now in North Carolina) to establish the Roanoke Colony.
* 1609 – Eighty Years' War: Spain and the Dutch Republic sign the Treaty of Antwerp to initiate twelve years of truce.
* 1682 – Robert Cavelier de La Salle discovers the mouth of the Mississippi River, claims it for France and names it Louisiana.
* 1782 – American War of Independence: Battle of the Saintes begins.
* 1860 – On his phonautograph machine, Édouard-Léon Scott de Martinville makes the oldest known recording of an audible human voice.
* 1852 – At a general conference of the The Church of Jesus Christ of Latter-day Saints, Brigham Young explains the Adam–God doctrine, an important part of the theology of Mormon fundamentalism.
* 1865 – American Civil War: Robert E. Lee surrenders the Army of Northern Virginia (26,765 troops) to Ulysses S. Grant at Appomattox Courthouse, Virginia, effectively ending the war.
* 1867 – Alaska purchase: Passing by a single vote, the United States Senate ratifies a treaty with Russia for the purchase of Alaska.
* 1909 – The U.S. Congress passes the Payne-Aldrich Tariff Act.
* 1914 – Mexican Revolution: One of the world's first naval/air skirmishes takes place off the coast of western Mexico.
* 1916 – World War I: The Battle of Verdun – German forces launch their third offensive of the battle.
* 1917 – World War I: The Battle of Arras – the battle begins with Canadian Corps executing a massive assault on Vimy Ridge.
* 1918 – World War I: The Battle of the Lys – the Portuguese Expeditionary Corps is crushed by the German forces during what is called the Spring Offensive on the Belgian region of Flanders.
* 1918 – The National Council of Bessarabia proclaims union with the Kingdom of Romania.
* 1937 – The Kamikaze arrives at Croydon Airport in London – it is the first Japanese-built aircraft to fly to Europe.
* 1939 – Marian Anderson sings at the Lincoln Memorial, after being denied the right to sing at the Daughters of the American Revolution's Constitution Hall.
* 1940 – World War II: Operation Weserübung – Germany invades Denmark and Norway.
* 1942 – World War II: The Battle of Bataan/Bataan Death March – United States forces surrender on the Bataan Peninsula. The Japanese Navy launches an air raid on Trincomalee in Ceylon (Sri Lanka); Royal Navy aircraft carrier HMS Hermes and Royal Australian Navy Destroyer HMAS Vampire are sunk off the island's east coast.
* 1945 – World War II: The German pocket battleship Admiral Scheer is sunk.
* 1945 – World War II: The Battle of Königsberg, in East Prussia, ends.
* 1945 – The United States Atomic Energy Commission is formed.
* 1947 – The Glazier-Higgins-Woodward tornadoes kill 181 and injure 970 in Texas, Oklahoma, and Kansas.
* 1947 – The Journey of Reconciliation, the first interracial Freedom Ride begins through the upper South in violation of Jim Crow laws. The riders wanted enforcement of the United States Supreme Court's 1946 Irene Morgan decision that banned racial segregation in interstate travel.
* 1948 – Jorge Eliécer Gaitán's assassination provokes a violent riot in Bogotá (the Bogotazo), and a further ten years of violence in Colombia known as La violencia.
* 1948 – Fighters from the Irgun and Lehi Zionist paramilitary groups attacked Deir Yassin near Jerusalem, killing over 100.
* 1952 – Hugo Ballivian's government is overthrown by the Bolivian National Revolution, starting a period of agrarian reform, universal suffrage and the nationalisation of tin mines
* 1957 – The Suez Canal in Egypt is cleared and opens to shipping.
* 1959 – Project Mercury: NASA announces the selection of the United States' first seven astronauts, whom the news media quickly dub the "Mercury Seven".
* 1961 – The Pacific Electric Railway in Los Angeles, once the largest electric railway in the world, ends operations.
* 1965 – Astrodome opens. First indoor baseball game is played.
* 1967 – The first Boeing 737 (a 100 series) makes its maiden flight.
* 1968 – Funeral of Martin Luther King, Jr.
* 1969 – The "Chicago Eight" plead not guilty to federal charges of conspiracy to incite a riot at the 1968 Democratic National Convention in Chicago, Illinois.
* 1969 – The first British-built Concorde 002 makes its maiden flight from Filton to RAF Fairford.
* 1975 – The first game of the Philippine Basketball Association, the second oldest professional basketball league in the world.
* 1975 – 8 people in South Korea, who are involved in People's Revolutionary Party Incident, are hanged.
* 1980 – The Iraqi regime of Saddam Hussein kills philosopher Muhammad Baqir al-Sadr and his sister Bint al-Huda after three days of torture.
* 1981 – The U.S. Navy nuclear submarine USS George Washington (SSBN-598) accidentally collides with the Nissho Maru, a Japanese cargo ship, sinking it.
* 1989 – The April 9 tragedy in Tbilisi, Georgian SSR an anti-Soviet peaceful demonstration and hunger strikes, demanding restoration of Georgian independence is dispersed by the Soviet army, resulting in 20 deaths and hundreds of injuries.
* 1992 – A U.S. Federal Court finds former Panamanian dictator Manuel Noriega guilty of drug and racketeering charges. He is sentenced to 30 years in prison.
* 1992 – John Major's Conservative Party wins an unprecedented fourth general election victory in the United Kingdom.
* 2003 – 2003 invasion of Iraq: Baghdad falls to American forces;Saddam Hussein statue topples as Iraqis turn on symbols of their former leader, pulling down the statue and tearing it to pieces.
* 2005 – Wedding of Charles, Prince of Wales and Camilla, Duchess of Cornwall; Charles, Prince of Wales marries Camilla Parker Bowles in a civil ceremony at Windsor's Guildhall.
* 2009 – In Tbilisi, Georgia, up to 60,000 people protest against the government of Mikheil Saakashvili.
* 2011 – A gunman murdered five people, injured eleven, and committed suicide in a mall in the Netherlands.