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was a leap year starting on Tuesday of the Gregorian calendar and a leap year starting on Sunday of the Julian calendar, the 1856th year of the Common Era (CE) and Anno Domini (AD) designations, the 856th year of the 2nd millennium, the 56th year of the 19th century, and the 7th year of the 1850s decade. As of the start of 1856, the Gregorian calendar was
12 days ahead of the Julian calendar, which remained in localized use until 1923.
- January 8 – Borax deposits are discovered in large quantities, by John Veatch in California.
- January 24 – U.S. President Franklin Pierce declares the new Free-State Topeka government in "Bleeding Kansas" to be in rebellion.
- January 26 – First Battle of Seattle: Marines from the USS Decatur suppress an indigenous uprising, in response to Governor Stevens' declaration of a "war of extermination" on Native communities.
- January 29
- February – The Tintic War breaks out in Utah.
- February 1 – Auburn University is first chartered, as the East Alabama Male College.
- February 2 – Dallas, Texas is incorporated as a city.
- February 7 – The nawab of Oudh (Wajid Ali Shah) is exiled to Metiabruz, and the state is annexed by the British East India Company.
- February 18 – The American Party (Know-Nothings) convenes in Philadelphia to nominate their first Presidential candidate, former President Millard Fillmore.
- March – Nepalese–Tibetan War: The signing of the Treaty of Thapathali concludes the war.
- March 5 – Fire destroys the Covent Garden Theatre in London.
- March 6 – Maryland Agricultural College (present-day University of Maryland, College Park) is chartered.
- March 20 – Filibuster War – Battle of Santa Rosa: Costa Rican troops rout Walker's soldiers.
- March 24 –Taiping Rebellion: Suspecting treachery on the part of East King Yang Xiuqing, Shi Dakai garrisons Anhui and begins his march back to the Heavenly Capital, having defeated a strong Xiang Army detachment.
- March 31 – The Treaty of Paris is signed, ending the Crimean War.
- April – The Xhosa cattle-killing movement and famine begins in Cape Colony.
- April 7 – Nelson College is founded in Nelson, New Zealand.
- April 10 – Theta Chi Fraternity is founded at Norwich University.
- April 16 – The Paris Declaration Respecting Maritime Law abolishes privateering, and regulates the relationship between neutral and belligerent and shipping on the high seas.
- April 17 – The Chicago Historical Society Museum is established at 1601 N. Clark Street, Chicago.
- April 21 – Building workers agitate for the eight-hour day in Melbourne, Australia.
- April 29 – The iron-hulled paddle steamer RMS Persia concludes a 9-day 16 hour westbound transatlantic crossing, at an average 13.11 knots (24.28 km/h), regaining the Blue Riband for the Cunard Line.
- May 1 – The province of Isabela is created in the Philippines, in honor of Queen Isabella II of Spain.
- May 3 – Queen Victoria of the United Kingdom gives Norfolk Island to the population of the colony at Pitcairn Island, most being descendants of the Mutiny on the Bounty. They first settle on Norfolk Island on June 8. Women's suffrage, as practiced on Pitcairn, is extended to Norfolk Island.
- May 14 – The San Francisco Committee of Vigilance is founded in the United States. It lynches two gangsters, arrests most Democratic Party officials, and disbands itself on August 18.
- May 20 – David Livingstone arrives at Quelimane on the Indian Ocean, having completed a 2-year transcontinental journey across Africa from Luanda.
- May 21 – Sacking of Lawrence: Lawrence, Kansas is captured and burned by pro-slavery forces.
- May 22 – Congressman Preston Brooks of South Carolina beats Senator Charles Sumner with a cane in the hall of the United States Senate, for a speech Sumner had made attacking Southerners who sympathized with the pro-slavery violence in Kansas ("Bleeding Kansas"). Sumner is unable to return to duty for 3 years while he recovers; Brooks becomes a hero across the South.
- May 24 – Pottawatomie massacre: A group of followers of radical abolitionist John Brown kill 5 homesteaders in Franklin County, Kansas.
- June 2 – Battle of Black Jack: Antislavery forces, led by John Brown, defeat proslavery forces in Bleeding Kansas.
- June 9 – 500 Mormon handcart pioneers leave Iowa City and head west for Salt Lake City, Utah, carrying all their possessions in two-wheeled handcarts.
- June 13 – Taiping Rebellion: Shi Dakai arrives at Nanjing.
- October 8 – The Second Opium War between several western powers and China begins, with the Arrow Incident on the Pearl River.
- October 13 – American mercenary William Walker effectively takes control of Nicaragua.
- November 1 – Anglo-Persian War: War is declared between Great Britain and Persia.
- November 4 – United States presidential election, 1856: Democrat James Buchanan defeats former President Millard Fillmore, representing a coalition of "Know-Nothings" and Whigs, and John C. Frémont of the fledgling Republican Party, to become the 15th President of the United States.
- November 11 – Taiping Rebellion: Shi Dakai arrives at the Heavenly Capital once more with 100,000 men, and demands that Wei Changhui and Qin Rigang be executed. Shi subsequently becomes head of the government.
- November 17 – American Old West: On the Sonoita River in present-day southern Arizona, the United States Army establishes Fort Buchanan, in order to help control new land acquired in the Gadsden Purchase.
- November 21 – Niagara University is founded in Niagara Falls, New York.
- November 27 – The Coup of 1856 leads to Luxembourg's unilateral adoption of a new, reactionary constitution, as King-Grand Duke William III signs the new constitution without the Chamber of Deputies' consent.
- December 1 – Under the County and Borough Police Act, in any county or area of England and Wales where a police force has not already been established, the Justices of the Peace must from this date take steps to create one according to nationally defined standards.
- December 2 – the National Portrait Gallery, London is established.
- December 9 – Bushehr surrenders to the British.
- January 9 – Lizette Woodworth Reese, American poet and teacher (d. 1935)
- January 11 – Christian Sinding, Norwegian composer (d. 1941)
- January 12 – John Singer Sargent, American artist (d. 1925)
- February 2
- February 5 – Frank Podmore, British psychical researcher (d. 1910)
- February 9 – Hara Takashi, Japanese politician, 10th Prime Minister of Japan (d. 1921)
- February 12 – Eduard von Böhm-Ermolli, Austrian general, German field marshal (d. 1941)
- February 14 – Frank Harris, Irish author, or (d. 1931)
- February 15 – Emil Kraepelin, German psychiatrist (d. 1926)
- February 20 – Prince Unakan Ananta Norajaya, Son of King Mongkut and Piam Sucharitakul (d. 1873)
- February 21 – Maurycy Gottlieb, Ukrainian painter (d. 1879)
- February 26 – Elizabeth Marney Conner, American elocutionist (unknown year of death)
- March 4
- March 8
- March 9
- March 16 – Napoléon Eugène Louis John Joseph, Prince Imperial, son of French Emperor Napoleon III (d. 1879)
- March 20
- March 26 – William Massey, 19th Prime Minister of New Zealand (d. 1925)
- April 5 – Booker T. Washington, American educator (d. 1915)
- April 6 – Maurice Sarrail, French general (d. 1929)
- April 12 – William Martin Conway, British art critic, mountaineer (d. 1937)
- April 18
- April 23 – Granville T. Woods, African-American inventor (d. 1910)
- April 24 – Philippe Pétain, French soldier, statesman (d. 1951)
- April 26 – Sir Joseph Ward, 17th Prime Minister of New Zealand (d. 1930)
- April 27 – Tongzhi Emperor of China (d. 1875)
- May 6
- May 8 – Pedro Lascuráin, 34th President of Mexico (d. 1952)
- May 13 – Fernando Tamagnini de Abreu e Silva, Portuguese general (d. 1924)
- May 15 – L. Frank Baum, American author, poet, playwright, actor and independent filmmaker (The Wizard of Oz) (d. 1919)
- May 21 – José Batlle y Ordóñez, Twice President of Uruguay (d. 1929)
- May 25
- June 14 – Andrey Markov, Russian mathematician (d. 1922)
- June 22 – H. Rider Haggard, English novelist (d. 1925)
- June 29 – Maria Cederschiöld, Swedish journalist (d. 1935)
- July 6 – Kate Simpson Hayes, Canadian playwright and legislative librarian (d. 1945)
- July 7 – Georg von der Marwitz, German general (d. 1929)
- July 10 – Nikola Tesla, Serbian-American inventor (d. 1943)
- July 11 – Georgiana Drew, American stage actress, married Maurice Barrymore in 1876 (d. 1893)
- July 23 – Bal Gangadhar Tilak, Indian political activist (d. 1920)
- July 24 – Franklin Ware Mann, American inventor (d. 1916)
- July 26 – George Bernard Shaw, Irish writer, Nobel Prize laureate (d. 1950)
- July 30 – Harriet Bates, American author (d. 1986)
- August 3 – Alfred Deakin, 2nd Prime Minister of Australia (d. 1919)
- August 10 – William Willett, British promoter of Daylight Saving Time (d. 1915)
- August 12 – Diamond Jim Brady, American businessman and philanthropist (d. 1917)
- August 15
- September 1 – Sergei Winogradsky, Russian scientist (d. 1953)
- September 3 – Louis Sullivan, American architect (d. 1924)
- September 18 – Wilhelm von Gloeden, German photographer (d. 1931)
- September 19 – Miguel R. Dávila, Honduranian general, 21st President of Honduras (d. 1927)
- September 27 – Bríet Bjarnhéðinsdóttir, Icelandic women's right activist (d. 1940)
- September 28 – Kate Douglas Wiggin, American author of Rebecca of Sunnybrook Farm (d. 1923)
- October 6 – William Shea, British actor (d. 1918)
- October 10 – George McClellan, U.S. House of Representatives from New York (d. 1927)
- October 21 – Francisco Plancarte y Navarrete, Mexican archaeologist and Roman Catholic archbishop of Monterrey, Mexico (d. 1920)
- October 23 – William Thomas Turner, British ship's captain with Cunard Steamship Company (d. 1933)
- October 30 – Charles Leroux, American balloonist, parachutist (d. 1889)
- November 13 – Louis Brandeis, Associate Justice of the Supreme Court of the United States (d. 1941)
- November 14
- November 16 – Jürgen Kröger, German architect (d. 1928)
- November 17 – Demetrio Castillo Duany, Cuban revolutionary, soldier, and politician (d. 1922)
- November 21 – William Emerson Ritter, American biologist (d. 1944)
- November 22 – Heber J. Grant, 7th president of The Church of Jesus Christ of Latter-day Saints (d. 1945)
- November 24 – Bat Masterson, American lawman (d. 1921)
- November 28 – Mary Catherine Crowley, American author (d. 1920)
- November 29 – Theobald von Bethmann-Hollweg, Chancellor of Germany (d. 1921)
- December 2 – Robert Kajanus, Finnish conductor, composer (d. 1933)
- December 6– Hans Molisch, Czech-Austrian botanist (d. 1937)
- December 10
- December 11
- December 13 – Svetozar Boroević, Austrian field marshal (d. 1920)
- December 18
- December 22 – Frank B. Kellogg, United States Secretary of State, recipient of the Nobel Peace Prize (d. 1937)
- December 23 – James Buchanan Duke, American tobacco and electric power industrialist (d. 1925)
- December 25 – Hans von Bartels, German painter (d. 1913)
- December 28 – Woodrow Wilson, 28th President of the United States, recipient of the Nobel Peace Prize (d. 1924)
- January 4 – Charles Brudenell-Bruce, 1st Marquess of Ailesbury, British politician (b. 1773)
- January 14 – Janko Drašković, Croatian politician, reformer (b. 1770)
- January 16 – Thaddeus William Harris, American naturalist (b. 1795)
- January 31 – Khedrup Gyatso, 11th Dalai Lama (b. 1838)
- February 4 – Anna Gottlieb, Austrian operatic soprano (b. 1774)
- February 17 – Heinrich Heine, German writer (b. 1797)
- May 3 – Adolphe Charles Adam, French composer (b. 1803)
- June 23 – Ivan Kireyevsky, Russian literary critic, philosopher (b. 1806)
- June 26 – Max Stirner, German philosopher (b. 1806)
- July 9 – Amedeo Avogadro, Italian chemist (b. 1776)
- July 11 – Norberto Ramírez, Central American politician
- July 14 – Edward Vernon Utterson, English lawyer, literary antiquary, collector and or (b. 1775/1776)
- July 20 – Anna Nielsen, Danish mezzo-soprano (b. 1803)
- July 29
- August 14 – William Buckland, English geologist, palaeontologist (b. 1784)
- August 19 – Anna Maria Rüttimann-Meyer von Schauensee, politically active Swiss salonist (b. 1772)
- August 29 – Mary Anne Schimmelpenninck, British Christian writer (b. 1778)
- August 30 – Gilbert Abbott à Beckett, English writer (b. 1811)
- September 3 – Honório Hermeto Carneiro Leão, Marquis of Paraná, Brazilian politician (b. 1801)
- October 19
- November 23 – Manuela Sáenz, Colombian national heroine (b. 1797)
- December 20 – Francesco Bentivegna, Italian revolutionary (b. 1820)