October 23 is the 296th day of the year in the Gregorian calendar. There are 69 days remaining until the end of the year.
42 BC – Liberators' civil war: Second Battle of Philippi: Mark Antony and Octavian decisively defeat Brutus's army. Brutus commits suicide.
425 – Valentinian III is elevated as Roman emperor at the age of six.
501 – The Synodus Palmaris, called by Gothic king Theoderic the Great, discharges Pope Symmachus of all charges, thus ending the schism of Antipope Laurentius.
1086 – At the Battle of Sagrajas, the army of Yusuf ibn Tashfin defeats the forces of Castilian King Alfonso VI.
1157 – The Battle of Grathe Heath ends the civil war in Denmark. King Sweyn III is killed and Valdemar I restores the country.
1295 – The first treaty forming the Auld Alliance between Scotland and France against England is signed in Paris.
1641 – Irish Catholic gentry from Ulster tried to seize control of Dublin Castle, the seat of English rule in Ireland, to force concessions to Catholics.
1642 – Battle of Edgehill: First major battle of the First English Civil War.
1694 – British/American colonial forces, led by Sir William Phips, fail to seize Quebec from the French.
1707 – The first Parliament of Great Britain meets.
1739 – War of Jenkins' Ear starts: British Prime Minister Robert Walpole, reluctantly declares war on Spain.
1812 – Claude François de Malet, a French general, begins a conspiracy to overthrow Napoleon Bonaparte, claiming that the Emperor died in Russia and that he is now the commandant of Paris.
1850 – The first National Women's Rights Convention begins in Worcester, Massachusetts, United States.
1861 – U.S. President Abraham Lincoln suspends the writ of habeas corpus in Washington, D.C., for all military-related cases.
1864 – American Civil War: Battle of Westport: Union forces under General Samuel R. Curtis defeat Confederate troops led by General Sterling Price at Westport, Missouri, near Kansas City.
1870 – Franco-Prussian War: The Siege of Metz concludes with a decisive Prussian victory.
1906 – Alberto Santos-Dumont flies an airplane in the first heavier-than-air flight in Europe at Champs de Bagatelle, Paris, France.
1911 – First use of aircraft in war: Italo-Turkish War: An Italian pilot takes off from Libya to observe Turkish army lines.
1912 – First Balkan War: The Battle of Kumanovo between the Serbian and Ottoman armies begins.
1915 – Women's suffrage: In New York City, 25,000–33,000 women march on Fifth Avenue to advocate their right to vote.
1917 – Lenin calls for the October Revolution.
1929 – Wall Street Crash of 1929. After a steady decline in stock market prices since a peak in September, the New York Stock Exchange begins to crash.
1935 – Dutch Schultz, Abe Landau, Otto Berman, and Bernard "Lulu" Rosencrantz are fatally shot at a saloon in Newark, New Jersey in what will become known as The Chophouse Massacre.
1939 – The Japanese Mitsubishi G4M twin-engine "Betty" Bomber makes its maiden flight.
1941 – World War II: Field Marshal Georgy Zhukov takes command of Red Army operations to prevent the further advance into Russia of German forces and to prevent the Wehrmacht from capturing Moscow.
1942 – World War II: Second Battle of El Alamein: At El Alamein in northern Egypt, the British Eighth Army under Field Marshal Montgomery begins a critical offensive to expel the Axis armies from Egypt.
1942 – All 12 passengers and crewmen aboard an American Airlines DC-3 airliner are killed when it is struck by a U.S. Army Air Forces bomber near Palm Springs, California.
1942 – World War II: The Battle for Henderson Field begins during the Guadalcanal Campaign and ends on October 26.
1944 – World War II: Battle of Leyte Gulf: The largest naval battle in history begins in the Philippines.
1946 – The United Nations General Assembly convenes for the first time, at an auditorium in Flushing, Queens, New York City.
1955 – Prime Minister Ngô Đình Diệm defeats former emperor Bảo Đại in a referendum and founds the Republic of Vietnam.
1955 – Saar Statute referendum, 1955 to decide if the Saar region is to become an independent territory under economic union with France. 67% of voters rejected the statute, leading to the reunification of the Saar with Germany in 1957.
1956 – Thousands of Hungarians protest against the government and Soviet occupation. (The Hungarian Revolution is crushed on November 4).
1958 – The Springhill Mine bump: An earthquake traps 174 miners in the No. 2 colliery at Springhill, Nova Scotia, the deepest coal mine in North America at the time. By November 1, rescuers from around the world had dug out 100 of the victims, marking the death toll at 74.
1965 – Vietnam War: The 1st Cavalry Division (United States) (Airmobile), in conjunction with South Vietnamese forces, launches a new operation seeking to destroy North Vietnamese forces in Pleiku in the II Corps Tactical Zone (the Central Highlands).
1970 – Gary Gabelich sets a land speed record in a rocket-powered automobile called the Blue Flame, fueled with natural gas.
1972 – Operation Linebacker, a US bombing campaign against North Vietnam in response to its Easter Offensive, ends after five months.
1973 – The Watergate scandal: US President Richard M. Nixon agrees to turn over subpoenaed audio tapes of his Oval Office conversations.
1982 – A gunfight breaks out between police officers and members of a religious cult known as the "Christ Miracle Healing Center and Church" in Miracle Valley, Arizona. The shootout leaves two cultists dead and dozens of cultists and police officers injured.
1983 – Lebanese Civil War: The U.S. Marines barracks in Beirut is hit by a truck bomb, killing 241 U.S. military personnel. A French army barracks in Lebanon is also hit that same morning, killing 58 troops.
1989 – The Hungarian Republic is officially declared by president Mátyás Szűrös, replacing the communist Hungarian People's Republic.
1989 – Bankruptcy of Wärtsilä Marine; the biggest bankruptcy in the Nordic countries until then.
1991 – Signing of the Paris Peace Accords which ended the Cambodian–Vietnamese War. Commemorated as a public holiday in Cambodia.
1993 – The Troubles: A Provisional IRA bomb prematurely detonates in the Shankill area of Belfast, killing the bomber and nine civilians.
1995 – Yolanda Saldívar is found guilty of first-degree murder in the shooting death of popular Latin singer Selena. Saldívar was sentenced to life in prison, eligible for parole in 2025.
1998 – Israeli–Palestinian conflict: Israeli Prime Minister Benjamin Netanyahu and Palestinian Chairman Yasser Arafat reach a "land for peace" agreement.
2002 – Moscow theater hostage crisis:
Chechen terrorists seize the House of Culture theater in Moscow and take approximately 700 theater-goers hostage.
2004 – A powerful earthquake and its aftershocks hit Niigata Prefecture in northern Japan, killing 35 people, injuring 2,200, and leaving 85,000 homeless or evacuated.
2007 – A powerful cold front in the Bay of Campeche causes the Usumacinta jackup rig to collide with Kab 101, leading to the death and drowning of 22 people during rescue operations after evacuation of the rig.
2011 – A powerful 7.2 magnitude earthquake strikes Van Province, Turkey, killing 582 people and injuring thousands.
2011 – The Libyan National Transition Council deems the Libyan Civil War over.
2012 – After 38 years, the world's first teletext service (BBC's Ceefax) ceases broadcast due to Northern Ireland completing the digital switchover.
2015 – The lowest sea-level pressure in the Western Hemisphere, and the highest reliably-measured non-tornadic sustained winds, are recorded in Hurricane Patricia, which strikes Mexico hours later, killing at least 13 and causing over $280 million in damages.
