1866
Events
January
- January 1
- * Fisk University, a historically black university, is established in Nashville, Tennessee.
- * The last issue of the abolitionist magazine The Liberator is published.
- January 6 – Ottoman troops clash with supporters of Maronite leader Youssef Bey Karam, at St. Doumit in Lebanon; the Ottomans are defeated.
- January 12
- * The Royal Aeronautical Society is formed as The Aeronautical Society of Great Britain in London, the world's oldest such society.
- * British auxiliary steamer sinks in a storm in the Bay of Biscay, on passage from the Thames to Australia, with the loss of 244 people, and only 19 survivors.
- January 18 – Wesley College, Melbourne, is established.
- January 26 – Volcanic eruption in the Santorini caldera begins.
February
- February 7 – Battle of Abtao: A Spanish naval squadron fights a combined Peruvian-Chilean fleet, at the island of Abtao, in the Chiloé Archipelago of southern Chile.
- February 13 – The first daylight bank robbery in United States history during peacetime takes place in Liberty, Missouri. This is considered to be the first robbery committed by Jesse James and his gang, although James's role is disputed.
- February 26 – The Calaveras Skull is discovered in California. Purported to be evidence of humans in North America during the Pliocene epoch, it turns out to be a hoax.
March
- March 13 – The United States Congress overwhelmingly passes the Civil Rights Act of 1866, the first federal legislation to protect the rights of African-Americans; U.S. President Andrew Johnson vetoes the bill on March 27, and Congress overrides the veto on April 9.
- March 31 – A total lunar eclipse occurs.
April
- April 4 - Alexander II of Russia narrowly escapes an assassination attempt in the city of St Petersburg.
- April 8 - The kingdoms of Italy and Prussia form an alliance against the Austrian Empire.
- April 10 - The American Society for the Prevention of Cruelty to Animals is founded in New York City by Henry Bergh.
May
- May 1-3 - The Memphis massacre: a rebellion with a series of violent racial events.
- May 2 - Battle of Callao: Peruvian defenders fight the Spanish fleet.
- May 7 - Student Ferdinand Cohen-Blind makes a failed attempt to assassinate Otto von Bismarck in Unter den Linden in Berlin.
File:ShieldNickel.jpeg|thumb|260px|right| May 16: U.S. nickel coin approved.
- May 10 - London bank Overend, Gurney and Company collapses, precipitating Panic of 1866.
- May 16 - The United States Congress approves the minting of a nickel 5-cent coin, eliminating its predecessor, the half dime.
- May 24 - Battle of Tuyutí: 32,000 soldiers of the Triple Alliance defeat 24,000 Paraguayan soldiers few miles north of the Paraná, Argentina, in the Paraguayan War, with 16,000 casualties.
- May 26 - First production of the comic opera Cox and Box by F. C. Burnand and Arthur Sullivan at Moray Lodge, Kensington
- May 30 - Bedrich Smetana's comic opera The Bartered Bride premiered in Prague.
June
- June 2 - Fenian forces skirmish with Canadian militia at the battles of Ridgeway and Fort Erie.
- June 5 - Calculations indicate Pluto reaches its only aphelion between 1618 and August 2113.
- June 8 - The Parliament of Canada meets for the first time in Ottawa.
- June 11 - The Agra High Court is established.
- June 14 - The Austro-Prussian War begins when the Austrians and most of the medium-size German states declare war on Prussia.
- June 20 - The Kingdom of Italy declares war on Austria.
- June 22 - In Sweden, the Riksdag of the Estates votes to replace itself by an elected two-chamber Riksdag.
- June 27-29 - Battle of Langensalza: The Prussians defeat the Hanoverian army.
July
- July 3 – Battle of Königgrätz: the Prussian army under King Wilhelm and Helmuth von Moltke defeats the Austrian army of Ludwig von Benedek, leading to a decisive Prussian victory in the Austro-Prussian War.
- July 5 – Princess Helena, third daughter of Queen Victoria, marries Prince Christian of Schleswig-Holstein.
- July 10 – Reconstruction Treaty with Choctaw & Chickasaw, completing the abolition of slavery in the United States; see also Choctaw freedmen.
- July 13 – The first Constitution of Romania is issued.
- July 20 – Austro-Prussian War: Naval Battle of Lissa – The Austrian fleet under Wilhelm von Tegetthoff defeats the Italian fleet of Carlo di Persano.
- July 22 – Austro-Prussian War: Battle of Blumenau – Austrians defend Bratislava against the Prussian army, concluding the fighting in the war.
- July 24 – Reconstruction: Tennessee becomes the first U.S. state to be readmitted to the Union following the American Civil War.
- July 25 – The United States Congress passes legislation authorizing the four-star rank of General of the Army ; Lieutenant General Ulysses S. Grant becomes the first to have this rank.
File:Atlantic cable Map.jpg|thumb|July 27: Atlantic Cable completed
- July 27 – The successfully completes laying the transatlantic telegraph cable between Valentia Island, Ireland, and Heart's Content, Newfoundland, permanently restoring a communications link.
- July 28 – The Metric Act of 1866 becomes law and legalizes the standardization of weights and measures in the United States.
August
- August 23 – The Treaty of Prague formally ends the Austro-Prussian War. The Duchy of Limburg leaves the German Confederation.
- September 22 – Paraguay successfully defends Curupayty against the Triple Alliance in the Paraguayan War, killing more than 5,000 while sustaining just about 50 casualties.
- September – The Great Tea Race of 1866 ends in London, narrowly won by the clipper ship Taeping.
October
- October 12 – The Treaty of Vienna ends the war between Austria and Italy; it formalizes the annexation of Venetia by Italy.
- October 14 – French troops under the command of Rear Admiral Pierre-Gustave Roze land at Ganghwa Island, Korea, as part of a punitive expedition against that kingdom for the execution of French Jesuit priests. It is the first military contact between Korea and a Western force.
- October 22 – The office of State President of the South African Republic is created by constitutional amendment approved at a session of the Volksraad.
November
- November 7 – The Ruse–Varna railway line officially opens.
December
- December 12– Oaks explosion: The worst mining disaster in England kills 383 miners and rescuers.
- December 18 – The College of Wooster is founded in Ohio.
Date unknown
- Federalist revolts occur in Argentina.
- Alfred Nobel invents dynamite in Germany.
- Foundation of the predecessors of Nestlé S.A., the Anglo-Swiss Milk Company and Farine Lactée Henri Nestlé.
- The Minneapolis Milling Company, predecessor of General Mills, builds its own mills.
- Marcus Jastrow arrives in the United States to become rabbi of Congregation Rodeph Shalom in Philadelphia.
- The recommendations of the state Girls' School Committee of 1866 result in a series of progressive reforms in women's rights in Sweden.
- The Famine of 1866–68 begins in Finland.
- Erasmus Jacobs discovers the Eureka Diamond near Hopetown on the banks of the Orange River in the Cape of Good Hope.
- Magirus Kommamditist, as predecessor of a major worldwide commercial vehicles manufacturing brand, Iveco, is founded in Baden-Württemberg, Germany.
Births
January–March
- January 10 – Hermanus Johannes Lovink, Dutch agriculturalist and politician
- January 13
- * George Gurdjieff, Russian spiritual teacher
- * Vasily Kalinnikov, Russian composer
- January 15
- * Nathan Söderblom, Swedish archbishop, recipient of the Nobel Peace Prize
- * Horatio Dresser, American New Thought religious leader and writer
- January 16 – Percy Pilcher, English inventor and pioneer aviator
- January 19 – Harry Davenport, American actor
- January 29
- * Romain Rolland, French writer, Nobel Prize laureate
- * Frank Tudor, Australian politician
- February 1 – Agda Meyerson, Swedish nurse and healthcare profession activist
- February 2 – Enrique Simonet, Spanish painter
- February 9 – George Ade, American writer, newspaper columnist and playwright
- February 18 – Janko Vukotić, Montenegrin general
- February 26 – Herbert Henry Dow, Canadian chemical industrialist
- March 5 – Arthur Leopold Busch, English-born American submarine pioneer
- March 7 – Hans Fruhstorfer, German lepidopterist
- March 13 – Friedrich Boedicker, German admiral
- March 15 – Matthew Charlton, Australian politician
- March 19 – Emilio De Bono, Italian general and fascist activist
- March 21
- * James Harbord, American general
- * Wakatsuki Reijirō, 25th and 28th Prime Minister of Japan
April–June
- April 1 – Ferruccio Busoni, Italian pianist and composer
- April 3 – J. B. M. Hertzog, Boer General and 3rd Prime Minister of South Africa
- April 8 – Alfred Allen, American actor
- April 13 – Butch Cassidy, American outlaw
- April 14 – Anne Sullivan, American tutor of Helen Keller
- April 17 – Ernest Starling, English physiologist
- April 18 – Yamaya Tanin, Japanese admiral
- April 21 – Josefa Toledo de Aguerri, Nicaraguan pioneer educator
- April 22 – Hans von Seeckt, German general
- April 24 – Ishii Kikujirō, Japanese diplomat
- May 10 – Richard H. Jackson, American four-star admiral
- May 17 – Erik Satie, French composer
- May 22 – Charles F. Haanel, American New Thought author and businessman
- June 4 – Miina Sillanpää, Finnish politician
- June 26
- * George Herbert, 5th Earl of Carnarvon, English financier of Egyptian excavations
- * Josef Swickard, German actor