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1868 (MDCCCLXVIII)was a leap year starting on Wednesday of the Gregorian calendar and a leap year starting on Monday of the Julian calendar, the 1868th year of the Common Era (CE) and Anno Domini (AD) designations, the 868th year of the 2nd millennium, the 68th year of the 19th century, and the 9th year of the 1860s decade. As of the start of 1868, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.
- January 2 – British Expedition to Abyssinia: Robert Napier leads an expedition to free captive British officials and missionaries.
- January 3 – The 15-year-old Mutsuhito, Emperor Meiji of Japan, declares the Meiji Restoration, his own restoration to full power, under the influence of supporters from the Chōshū and Satsuma Domains, and against the supporters of the Tokugawa shogunate, triggering the Boshin War.
- January 5 – Paraguayan War: Brazilian Army commander Luís Alves de Lima e Silva, Duke of Caxias enters Asunción, Paraguay's capital. Some days later he declares the war is over. Nevertheless, Francisco Solano López, Paraguay's president, prepares guerrillas to fight in the countryside.
- January 7 – The Arkansas constitutional convention meets in Little Rock.
- January 9 – Penal transportation from Britain to Australia ends, with arrival of the convict ship Hougoumont in Western Australia, after an 89-day voyage from England. There are 62 Fenians among the transportees.
- January 10 – Shōgun Tokugawa Yoshinobu declares the emperor's declaration "illegal", and prepares to attack Kyoto.
- January 27–31 – Battle of Toba–Fushimi: forces of the Tokugawa shogunate and the allied pro-Imperial forces of the Chōshū, Satsuma and Tosa Domains clash near Fushimi, Kyoto, ending in a decisive victory for the Imperial forces (although in the January 28 naval Battle of Awa, the Shogunate is victorious against Satsuma).
- February – Foreign ministers meeting in Hyōgo are persuaded to recognise the restored Emperor Meiji of Japan, with promises that harbours will be open in accordance with international treaties.
- February 13 – The British War Office sanctions the formation of what becomes the Army Post Office Corps.
- February 16 – In New York City the Jolly Corks organization is renamed the Benevolent and Protective Order of Elks (BPOE).
- February 19 – In the Passage of Humaitá, a Brazilian naval force succeeds in dashing past a Paraguayan fortress on the River Paraguay, considered by some the turning point in the Paraguayan War.
- February 24
- March – French geologist Louis Lartet discovers the first identified skeletons of Cro-Magnon, the first early modern humans (early Homo sapiens sapiens), at Abri de Crô-Magnon, a rock shelter at Les Eyzies, Dordogne, France.
- March 12
- March 23 – The University of California is founded in Oakland, California, when the Organic Act is signed into California law.
- March 24 – The Metropolitan Life Insurance Company is formed, in New York City.
- March 27 – The Lake Ontario Shore Railroad Company is organized in Oswego, New York.
- March – The first transnational women's organization, Association internationale des femmes, is founded.
- April 1 – The Hampton Normal and Agricultural Institute is established in Hampton, Virginia.
- April 7 – The Charter Oath, drawn up by his councilors, is promulgated at the enthronement of the Emperor Meiji of Japan, promising deliberative assemblies and an end to feudalism.
- April 9 – Emperor Tewodros II of Ethiopia massacres at least 197 of his own people at Magdala. These are prisoners incarcerated, for the most part, for very trivial offenses, and are killed for requesting bread and water.
- April 9–13 – Battle of Magdala: A British-Indian task force under Robert Napier inflicts 700 deaths and a crushing defeat on the army of Emperor Tewodros II; the British and Indians suffer 30 wounded, two of whom die subsequently. Tewodros commits suicide and Magdala is captured, ending the British Expedition to Abyssinia.
- April 11 – July – Fall of Edo: The Japanese city surrenders to Emperor Meiji. Shōgun Tokugawa Yoshinobu submits to the Emperor.
- April 29 – General William Tecumseh Sherman brokers the Treaty of Fort Laramie, between the federal government of the United States and the Plains Indians.
- May 10–14 – Boshin War – Battle of Utsunomiya Castle, Japan: Forces of the Emperor Meiji resist the retreating troops of the Tokugawa shogunate.
- May 16, May 26 – President Andrew Johnson is twice acquitted during his impeachment trial, by one vote in the United States Senate.
- May 26 – Fenian bomber Michael Barrett becomes the last person publicly hanged in the United Kingdom.
- May 29 – The Parliament of the United Kingdom passes the Capital Punishment Amendment Act, thus ending public hanging.
- May 30 – Memorial Day is observed in the United States for the first time (it was proclaimed on May 5 by General John A. Logan).
- May 31
- June – Tītokowaru's War breaks out in the South Taranaki District of New Zealand's North Island between the Ngāti Ruanui Māori tribe and the New Zealand Government.
- June 1 – The Treaty of Bosque Redondo is signed, allowing the Navajo to return to their lands in Arizona and New Mexico.
- June 2 – The first Trades Union Congress is held in Manchester, England.
- June 10 – Mihailo Obrenović, Prince of Serbia is assassinated in Košutnjak, Belgrade.
- June 20 – Fort Fred Steele is established to protect what is at this time the western terminus of the Union Pacific Railway, near modern-day Sinclair, Wyoming.
- July 1 – The cable-operated West Side and Yonkers Patent Railway in Manhattan becomes the first elevated railway in the United States.
- July 4 – Battle of Ueno: Imperial Japanese troops defeat the Shōgitai (elite forces remaining loyal to the shōgun).
- July 5 – Preacher William Booth establishes the Christian Mission, predecessor of The Salvation Army, in the East End of London.
- July 9 – The Fourteenth Amendment to the United States Constitution is ratified.
- July 18 – The Navajo people begin their long march home.
- July 25 – Wyoming becomes a United States territory.
- July 25 – Paraguayan War: The Allies, in an amphibious operation, capture the fortress of Humaitá.
- July 27 – The United States Expatriation Act ("An Act concerning the Rights of American Citizens in foreign States") is adopted.
- July 28 – The Fourteenth Amendment to the United States Constitution is adopted, including the Citizenship Clause and the Equal Protection Clause, legally, if not actually, guaranteeing African Americans full citizenship and equal protection, and all persons in the United States due process of law.
- August 13 – The 8.5–9.0 Mw Arica earthquake strikes southern Peru, with a maximum Mercalli intensity of XI (Extreme), causing 25,000+ deaths and a destructive basin-wide tsunami, that affects Hawaii and New Zealand.
- August 18 – The element later named as helium is first detected in the spectrum of the Sun's chromosphere, by French astronomer Jules Janssen, during a total eclipse in Guntur, British India, but is assumed to be sodium.
- August 20 – Abergele rail disaster in Wales: An Irish Mail passenger train collides with 4 cargo trucks loaded with paraffin oil (more akin to modern kerosine); 33 are killed (the first major train disaster in Britain).
- August 22 – The Yangzhou riot in China targets a station of the China Inland Mission, and nearly leads to war between Britain and China.
- September – Glorious Revolution: Queen Isabella II of Spain is effectively deposed and sent into exile; she formally abdicates on June 25, 1870.
- September 3 – Emperor Meiji of Japan announces that the name of the city of Edo is to be changed to Tokyo.
- September 7 – Tītokowaru's War: Māori leader Titokowaru defeats a New Zealand military force at Te Ngutu o Te Manu, North Island.
- September 18 – The University of the South holds its first convocation in Sewanee, Tennessee.
- September 23 – Grito de Lares: Rebels (some 400–600 led by Ramón Emeterio Betances) in the town of Lares declare Puerto Rico independent; the local militia easily defeats them a week later.
- September 24 – Croatian–Hungarian Settlement (Croatian: Hrvatsko-ugarska nagodba, Hungarian: Horvát–magyar kiegyezés, German: Kroatisch-Ungarischer Ausgleich) is concluded, governing Croatia's political status in the Hungarian-ruled part of Austria-Hungary until 1918.