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1856 (MDCCCLVI)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.
беларуская (тарашкевіца): 1856
srpskohrvatski / српскохрватски: 1856