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1849 (MDCCCXLIX) was a common year starting on Monday of the Gregorian calendar and a common year starting on Saturday of the Julian calendar, the 1849th year of the Common Era (CE) and Anno Domini (AD) designations, the 849th year of the 2nd millennium, the 49th year of the 19th century, and the 10th and last year of the 1840s decade. As of the start of 1849, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.
- January 1 – France begins issue of the Ceres series, the nation's first postage stamps.
- January 5 – Hungarian Revolution of 1848: The Austrian army, led by Alfred I, Prince of Windisch-Grätz, enters in the Hungarian capitals, Buda and Pest. The Hungarian government and parliament flee to Debrecen.
- January 8 – Hungarian Revolution of 1848: Romanian armed groups massacre 600 unarmed Hungarian civilians, at Nagyenyed.
- January 13
- January 21
- January 23 – Elizabeth Blackwell is awarded her M.D. by the Medical Institute of Geneva, New York, thus becoming the United States' first woman doctor.
- January 27 – The Fayetteville and Western Plank Road Company is incorporated, to build a plank road from Fayetteville to Bethania, North Carolina.
- January 31 – Hungarian Revolution of 1848: A Russian army of 10,000 soldiers enters Transylvania, in order to help the Austrians defeat the Hungarian forces, led by Josef Bem.
- February 1 – The abolition of the Corn Laws by the United Kingdom's Importation Act 1846 comes fully into effect.
- February 2 – Treaty of Guadalupe Hidalgo signed, ending the Mexican–American War (effective on exchange of ratifications, May 30; proclaimed July 4).
- February 4 – Hungarian Revolution of 1848: Battle of Vízakna – The Austrian army, led by Anton Puchner, defeats the Hungarians, led by general Josef Bem.
- February 5 – Hungarian Revolution of 1848: The Hungarian revolutionary army, led by Richard Guyon, breaks through the pass of Branyiszkó, defeating the Austrian defenders.
- February 8 – The new Roman Republic is proclaimed.
- February 9 – Hungarian Revolution of 1848: Battle of Piski – Josef Bem's Hungarian army defeats Anton Puchner.
- February 14 – In New York City, James Knox Polk becomes the first President of the United States to have his photograph taken.
- February 21 – Second Anglo-Sikh War: Battle of Gujrat – Forces of the British East India Company defeat those of the Sikh Empire in Punjab.
- February 27 – Hungarian Revolution of 1848: Battle of Kápolna – The Austrians defeat the Hungarians.
- February 28 – Regular steamboat service from the west to the east coast of the United States begins, with the arrival of the SS California in San Francisco Bay. The California leaves New York Harbor on October 6, 1848, rounds Cape Horn at the tip of South America, and arrives at San Francisco after the 4-month, 21-day journey.
- March – The Frankfurt Parliament completes its drafting of a liberal constitution, and elects Frederick William IV emperor of the new German national state.
- March 3
- March 4
- March 5
- March 11 – Hungarian Revolution of 1848: The Hungarian army of Transylvania, under general Josef Bem, defeats the Russian-Austrian army at Nagyszeben, capturing the city which is the headquarters of Austrian general Anton Puchner. Most of Transylvania is liberated from the Austrian rule. The Austrian and the Russian troops flee to Wallachia.
- March 28 – Four Christians are ordered burnt alive in Antananarivo, Madagascar, by Queen Ranavalona I, and 14 others are executed.
- March 30 – The Second Anglo-Sikh War ends, with the United Kingdom annexing the Punjab.
- March 30 - Maharaja Duleep Singh is exiled to England.
- April 1
- April 2 – The German revolutions of 1848–49 end in failure, as King Frederick William IV of Prussia refuses to accept the offer of the Frankfurt National Assembly, to be crowned as German emperor.
- April 4 – Hungarian Revolution of 1848 – Battle of Tápióbicske: Hungarian forces, under the generals György Klapka and János Damjanich, defeat the Austrian-Croatian army, led by Franz Schlik and Josip Jelačić.
- April 6 – Hungarian Revolution of 1848 – Battle of Isaszeg: The main Hungarian forces, led by Arthur Görgey, defeat the main imperial forces, led by Alfred I, Prince of Windisch-Grätz, forcing them to retreat westward.
- April 10 – Hungarian Revolution of 1848 – First Battle of Vác: The Hungarians, led by János Damjanich, defeat the Austrians, led by Christian Götz, who dies after the battle due to his injuries.
- April 12 – Hungarian Revolution of 1848: Because of his series of defeats suffered from the Hungarian army, Alfred I, Prince of Windisch-Grätz is released from the supreme command of the Austrian forces in Hungary, and replaced by Ludwig von Welden.
- April 14 – Hungarian Revolution of 1848: The Hungarian revolutionary parliament in Debrecen declares independence from the Habsburg Empire.
- April 19 – Hungarian Revolution of 1848 – Battle of Nagysalló: The Hungarian revolutionary army, led by György Klapka and János Damjanich, defeat the Austrian army, led by Lt. Gen. Ludwig von Wohlgemuth.
- April 21
- April 22 – The first Kennedy arrives in America.
- April 25 – James Bruce, 8th Earl of Elgin, the Governor General of Canada, signs the Rebellion Losses Bill, outraging Montreal's English population and triggering the Montreal Riots.
- April 26 – Hungarian Revolution of 1848 – Battle of Komárom: Hungarian forces relieve the city and castle with the same name from a long Austrian siege. The Austrian imperial forces and their Croatian, Romanian and Serbian allies are chased out from Hungary, or near the borders of the country.
- April 27 – Giuseppe Garibaldi enters Rome, to defend it from the French troops of General Charles Oudinot.
- May – The Second Carlist War ends in Spain.
- May 2 – Hungarian Revolution of 1848: A new independent Hungarian government, led by Bertalan Szemere, is formed. The head of state of Hungary becomes Lajos Kossuth, as governor president.
- May 3
- May 9 – The May Uprising in Dresden is suppressed by the Kingdom of Saxony.
- May 10 – The Astor Place Riot takes place in Manhattan, over a dispute between two Shakespearean actors; over 20 people are killed.
- May 15 – Troops of the Kingdom of the Two Sicilies take Palermo, and crush the republican government of Sicily.
- May 17 – The St. Louis Fire starts, when a steamboat catches fire and nearly burns down the entire city.
- May 21 – Hungarian Revolution of 1848: The Hungarian army, led by Arthur Görgey, captures the Castle of Buda, liberating the Hungarian capital city completely. The leader of the defending Austrian forces, General Heinrich Hentzi, dies because of his injuries. The Hungarian government moves back from Debrecen to Budapest.
- May 30 – Hungarian Revolution of 1848: Julius Jacob von Haynau replaces Ludwig von Welden as leader of the Austrian forces in Hungary, because of the failure of the latter to stop the advance of the Hungarian forces.
- June 5
- June 6 – The settlement of Fort Worth, Texas, is founded.
- June 17 – Hungarian Revolution of 1848: The main Russian forces, led by Ivan Paskevich, cross the Hungarian border, and together with the Austrian troops, led by Julius Jacob von Haynau, start the final attack against the Hungarian Revolution. Now the Hungarian revolutionary troops, numbering 173,000 soldiers, which even before the Russian attack were in inferiority regarding their numbers, and the quality of their weapons and war industry, face a force of 370,000 Austro-Russian forces, and other tens of thousands of Croatian, Serbian and Romanian insurgents, who serve the Habsburg imperial interests.
- June 20 – Hungarian Revolution of 1848: Russian troops, under the command of Alexander von Lüders, break in Transylvania, and together with the Austrian forces, start to operate against the Hungarian troops, led by Józef Bem.
- June 21 – Hungarian Revolution of 1848: The Russo-Austrian army, led by Julius Jacob von Haynau, defeats the Hungarians under the command of Arthur Görgey at Pered.
- June 28 – Hungarian Revolution of 1848: The Austrian army, led by Julius Jacob von Haynau, defeats the Hungarians, led by Ernő Poeltenberg, at Győr. The Hungarian army is forced to retreat towards Budapest.
- July 2 – Hungarian Revolution of 1848 – Second Battle of Komárom: The Hungarian army, led by Arthur Görgey, repulses the combined attack of the Austrian and Russian troops led by Julius Jacob von Haynau. During the battle Görgey suffers a heavy head injury, which prevents him from taking advantage of this success.
- July 3 – French troops occupy Rome; the Roman Republic surrenders.
- July 6 – Battle of Fredericia: The Danish Army beats the Prussian army at Fredericia, Jutland, thereby putting an end to the Prussian-Danish War until 1864.
- July 11 – Hungarian Revolution of 1848 – Third Battle of Komárom: The Hungarian army, led by Arthur Görgey, is defeated by the Austrians, led by Julius Jacob von Haynau.
- July 14
- July 17 – Hungarian Revolution of 1848: Hungarians, led by Arthur Görgey, and the Russians, led by Ivan Paskevich, battle indecisively at Vác. The Russians are unsuccessful in destroying the Hungarian army, which retreats towards the east.
- July 23 – The French scientist Hippolyte Fizeau measures the speed of light, with an instrument placed on the Earth.
- July 28 – Hungarian Revolution of 1848: The Hungarian government, led by Bertalan Szemere promulgates the Nationality Law, which gives important rights to the nationalities of Hungary, like the right to use their mother tongue in school, church, army, court and administration. The Romanians are declared a nation, and not a minority, in Transylvania. The Jews receive equality thanks to the Emancipation Decree.
- July 31 – Hungarian Revolution of 1848 – Battle of Segesvár: The Russian troops in Transylvania, led by Alexander von Lüders, crush the Hungarian forces, under the lead of Józef Bem. Hungarian poet and revolutionary Sándor Petőfi is killed in the battle by the Russians.
- July 31–August 1 – Joven Daniel wrecks at the coast of Araucanía, Chile, leading to allegations that local Mapuche tribes murdered survivors and kidnapped Elisa Bravo.
- August 2 – Hungarian Revolution of 1848: The Russian main forces, under Ivan Paskevich, defeat the Hungarian army under József Nagysándor, at Debrecen.
- August 3 – Hungarian Revolution of 1848: The Hungarian defenders of Komárom, led by György Klapka, destroy the besieging Austrian forces, liberating Győr and Székesfehérvár. But this victory comes too late to change the course of military events in the eastern part of the country, where the Hungarian forces are about to crumble under the heavy Austro-Russian pressure.
- August 5 – Hungarian Revolution of 1848 – Battle of Szőreg: Austrian forces, under Julius Jacob von Haynau, defeat the Hungarian main forces under Henryk Dembiński.
- August 9 – Hungarian Revolution of 1848 – Battle of Temesvár: The main Russo-Austrian forces, led by Julius Jacob von Haynau, win a decisive victory against the Hungarians, led by Józef Bem.
- August 11 – Hungarian Revolution of 1848: Lajos Kossuth and the Hungarian Government of Bertalan Szemere resign, and give all powers to the hands of Arthur Görgey. After this Kossuth, the ministries and many military officers leave Hungary, and ask asylum in Turkey.
- August 13 – Hungarian Revolution of 1848: The main Hungarian army, under the lead of Arthur Görgey, capitulates to the Russian troops, led by Theodor von Rüdiger, at Világos, ending the Hungarian Revolution.
- August 28 – Venice (the Republic of San Marco) surrenders to Austrian troops after a 4-month siege.
- September 1 – The first segment of the Pennsylvania Railroad, from Lewistown to Harrisburg, opens for service.
- September 17 – African-American abolitionist Harriet Tubman escapes from slavery.
- October 4 – Hungarian Revolution of 1848: Komárom, the last bastion of the Hungarian Revolution, surrenders to the Austrian forces.
- October 6
- November – Austin College receives a charter in Huntsville, Texas.
- November 13 – The Constitution of California is ratified in a general election.
- November 13 – Public hanging in London attended by 30,000-50,000 of George and Maria Manning.
- November 16 – A Russian court sentences Fyodor Dostoyevsky to death, for anti-government activities linked to a radical intellectual group, the Petrashevsky Circle. Facing a firing squad on December 23, the group members are reprieved at the last moment, and exiled to the katorga prison camps in Siberia.
- December 3 – German missionaries Johann Ludwig Krapf and Johannes Rebmann become the first Europeans to see Mount Kenya. The Abgeordnetenhaus, lower house of the parliament of the Kingdom of Bavaria, passes a bill granting German Jews the same legal rights as German Christians. The measure draws a strong reaction from Christians across Bavaria, who sign petitions urging the upper house to prevent the equal rights measure from becoming law.
- December 22 – After 17 days of deadlock and 63 votes, Democrat Howell Cobb of Georgia is elected Speaker of the United States House of Representatives, by a plurality of 102 votes to 99 for the former Speaker, the Whig Party's Robert C. Winthrop of Massachusetts. Neither the Democrats nor the Whigs have a majority of the 230 seats in the House, and after neither candidate can obtain the required 116 votes, the Representatives agree that the plurality will decide the leadership.
- The North Carolina General Assembly incorporates the North Carolina Railroad, to complete a rail line from Goldsboro through Raleigh, and Salisbury to Charlotte.
- Seven of the "best known" opium clippers go missing: Sylph, Coquette, Kelpie, Greyhound, Don Juan, Mischief, and Anna Eliza.
- Global healthcare and pharmaceutical company, Pfizer, founded in New York, United States.