1947 – Texas City Disaster: An explosion on board a freighter in port causes the city of Texas City, Texas, to catch fire, killing almost 600
1947 – Bernard Baruch coins the term "Cold War" to describe the relationship between the United States and the Soviet Union
1962 – from the USSR was sent the world's first SETI message.
1990 – The "Doctor of Death", Jack Kevorkian, participates in his first assisted suicide
2007 – Virginia Tech massacre: The deadliest spree killing in modern American history. Seung-Hui Cho, kills 32 and injures 23 before committing suicide.
1492 – Spain and Christopher Columbus sign the Capitulations of Santa Fe for his voyage to Asia to acquire spices.
1521 – Martin Luther speaks to the assembly at the Diet of Worms, refusing to recant his teachings.
1797 – Sir Ralph Abercromby attacks San Juan, Puerto Rico in what would be one of the largest invasions of the Spanish territories in America.
1895 – The Treaty of Shimonoseki between China and Japan is signed. This marks the end of the First Sino-Japanese War, and the defeated Qing Empire is forced to renounce its claims on Korea and to concede the southern portion of the Fengtien province, Taiwan and the Pescadores Islands to Japan.
1905 – The Supreme Court of the United States decides Lochner v. New York which holds that the "right to free contract" is implicit in the due process clause of the Fourteenth Amendment of the United States Constitution.
1924 – Metro-Goldwyn-Mayer studios is formed by the merger of Metro Pictures, Goldwyn Pictures, and the Louis B. Mayer Company.
1961 – Bay of Pigs Invasion: A group of CIA financed and trained Cuban refugees lands at the Bay of Pigs in Cuba with the aim of ousting Fidel Castro.
1964 – The Ford Motor Company unveils the Ford Mustang at the New York World's Fair.
1969 – Sirhan Sirhan is convicted of assassinating Robert F. Kennedy.
1970 – Apollo program: The ill-fated Apollo 13 spacecraft returns to Earth safely.
1975 – The Cambodian Civil War ends. The Khmer Rouge captures the capital Phnom Penh and Cambodian government forces surrender.
1982 – Patriation of the Canadian constitution in Ottawa by Proclamation of Queen Elizabeth II, Queen of Canada.
1986 – The Three Hundred and Thirty Five Years' War between the Netherlands and the Isles of Scilly ends.
1775 – American Revolution: The British advancement by sea begins; Paul Revere and other riders warn the countryside of the troop movements.
1783 – Fighting ceases in the American Revolution, eight years to the day since it began.
1902 – Quetzaltenango, second largest city of Guatemala, destroyed by Earthquake.
1906 – The 1906 San Francisco earthquake and fire destroys much of San Francisco, California.
1923 – Yankee Stadium, "The House that Ruth Built," opens
1930 – BBC Radio announces that there is no news on that day.
1942 – World War II: The Doolittle Raid on Japan. Tokyo, Yokohama, Kobe and Nagoya bombed.
1943 – World War II: Operation Vengeance, Admiral Isoroku Yamamoto is killed when his aircraft is shot down by U.S. fighters over Bougainville Island.
1954 – Gamal Abdal Nasser seizes power in Egypt.
1958 – A United States federal court rules that poet Ezra Pound is to be released from an insane asylum.
1980 - The Republic of Zimbabwe (formerly Rhodesia) comes into being, with Canaan Banana as the country's first President. The Zimbabwe Dollar replaces the Rhodesian Dollar as the official currency of Zimbabwe.
1983 – A suicide bomber destroys the United States embassy in Beirut, Lebanon, killing 63 people.
1988 – The United States launches Operation Praying Mantis against Iranian naval forces in the largest naval battle since World War II.
1996 – In Lebanon, at least 106 civilians are killed when the Israel Defense Forces shell the UN compound at Quana where more than 800 civilians had taken refuge.
Earliest day on which First Day of Summer or Sumardagurinn fyrsti can fall, while April 25 is the latest; celebrated on the first Thursday after April 18. (Iceland)
1775 – American Revolutionary War: The war begins with the battles of Lexington and Concord.
1936 – First day of the Great Uprising in Palestine.
1943 – World War II: In Poland, German troops enter the Warsaw ghetto to round up the remaining Jews, beginning the Warsaw Ghetto Uprising.
1943 – Bicycle Day – Swiss chemist Dr. Albert Hofmann deliberately takes LSD for the first time.
1960 – Students in South Korea hold a nationwide pro-democracy protest against their president Syngman Rhee, eventually forcing him to resign
1961 – The Bay of Pigs invasion of Cuba ends in success for the defenders.
1971 – Charles Manson is sentenced to death for the Sharon Tate murders.
1987 – The Simpsons premieres as a short cartoon on The Tracey Ullman Show
1989 – A gun turret explodes on the USS Iowa, killing 47 sailors.
1993 – The 51-day siege of the Branch Davidian building outside Waco, Texas, USA, ends when a fire breaks out. Eighty-one people die.
1993 – South Dakota governor George Mickelson and seven others are killed when a state-owned aircraft crashes in Iowa.
1995 – Oklahoma City bombing: The Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma, USA, is bombed, killing 168. That same day convicted murderer Richard Wayne Snell, who had ties to one of the bombers, Timothy McVeigh, is executed in Arkansas.
1999 – The German Bundestag returns to Berlin, the first German parliamentary body to meet there since the Reichstag was dissolved in 1945.
1657 – Freedom of religion is granted to the Jews of New Amsterdam (later New York City).
1775 – American Revolutionary War: the Siege of Boston begins, following the battles at Lexington and Concord
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.
1871 – The Civil Rights Act of 1871 becomes law.
1884 – Pope Leo XIII publishes the encyclical Humanum Genus.
1914 – 19 men, women, and children die in the Ludlow Massacre during a Colorado coal-miner's strike.
1918 – Manfred von Richthofen, aka The Red Baron, shoots down his 79th and 80th victims marking his final victories before his death the following day.
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
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.
1961 – Failure of the Bay of Pigs Invasion of US-backed troops against Cuba
1978 – Korean Air Flight 902 is shot down by Soviets.
1985 – ATF raid on The Covenant, The Sword, and the Arm of the Lord compound in northern Arkansas.
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,
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
2010 – Deepwater Horizon drilling rig explosion kills 11 and causes rig to sink, initiating a massive oil discharge in the Gulf of Mexico.