1900

1845–1958	Germany [earth sciences]	German naturalist and explorer Alexander von Humboldt lays the basis of modern geography with the publication of Kosmos/Cosmos, in which he arranges geographic knowledge in a systematic fashion.
1899–1900	Crete [archaeology]	British archaeologist Arthur John Evans excavates the palace of Knossos, Crete.
c. 1900	Persia, Iran [births and deaths]	Ruhollah Khomeini (Ruholla Hendi), Persian Shiite Muslim, organizer of the 1979 revolution after which he became political and religious leader of Iran for life, born in Khomeyn, Persia (–1989).
1900	Netherlands, Gemany, Austria [biology]	Dutch geneticist Hugo Marie de Vries, German botanist Carl Erich Correns, and Austrian botanist Erich Tschermak von Seysenegg, simultaneously and independently, rediscover the Austrian monk Gregor Mendel's 1865 work on heredity.
1900	France [cinema and film]	The Lumière Brothers Cinématograph is the highlight at the Paris International Exhibition. Primitive colour and sound film systems are also demonstrated.
1900	Belgium [civic and commercial buildings]	The Maison du Peuple in Brussels, Belgium, designed by the Belgian architect Victor Horta, is completed.
1900	USA [communications]	Canadian-born US scientist Reginald Aubrey Fessenden discovers the principle of amplitude modulation (AM) of radio waves.
1900	USA [fiction]	The US author Frank L Baum writes the children's classic The Wizard of Oz.
1900	USA [statistics and demography]	The population of the USA is more than 75 million.
1900	world [statistics and demography]	The world population stands at 1.6 billion.
1900	France [food and drink]	French tyre manufacturers André and Edouard Michelin launch the Guide Michelin, the first systematic guidebook to restaurants, hotels, and garages in Europe.
1900	USA [medicine]	US army pathologist Walter Reed establishes that yellow fever is caused by the bite of an Aëdes aegypti mosquito infected with the yellow fever parasite. His discovery leads to the creation of a vaccine and makes possible the completion of the Panama Canal.
1900	USA [motor vehicles]	There are now 8,000 cars on the roads in the USA.
1900	UK [newspapers]	The Daily Mail becomes the first newspaper in Britain to attain a circulation of 1 million.
1900	UK [newspapers]	Cyril Arthur Pearson publishes the Express in Britain; one of the paper's innovations is to have news on the front page.
1900	Italy [opera]	The opera Tosca by the Italian composer Giacomo Puccini is first performed, in Rome, Italy.
1900	Finland [orchestral music]	The Finnish composer Jean Sibelius completes his orchestral work Finlandia.
1900	England [orchestral music]	The English composer Edward Elgar completes his oratorio The Dream of Gerontius, based on a dramatic monologue by the English churchman Cardinal Newman.
1900	USA [telephone services]	There are now over 1,300,000 telephones in use in the USA.
1900	France [physics]	French physiologist Paul Ulrich Villard discovers a new type of radiation that is later known as gamma rays.
1900	Germany [physics]	German physicist Max Planck suggests that black bodies (perfect absorbers) radiate energy in packets or quanta, rather than continuously. He thus begins the science of quantum physics, which revolutionizes the understanding of atomic and subatomic processes.
1900	Norway [consumer products]	Norwegian Johann Vaaler patents paper clips in Germany.
1900	Austria [psychology]	The Austrian psychiatrist Sigmund Freud publishes Die Traumdeutung/The Interpretation of Dreams.
10 January 1900	South Africa [Anglo–Boer Wars (1899–1902)]	Following four months of Boer advances in the Second Anglo-Boer War, Field Marshal Frederick, Lord Roberts (‘Bobs’) lands in southern Africa as the new commander in chief of the British army, with Horatio, Lord Kitchener, as chief of staff.
25 January 1900	South Africa [Anglo–Boer Wars (1899–1902)]	In the Battle of Spion Kop in the Second Anglo-Boer War, a Boer army forces the British troops under General Sir Redvers Buller to retreat with heavy losses.
29 January 1900	USA [baseball]	Bancroft Byron ‘Ban’ Johnson founds the American League of Professional Baseball Clubs in Chicago, Illinois, as a rival to the National Baseball League.
28 February 1900	Natal [Anglo–Boer Wars (1899–1902)]	General Sir Redvers Buller relieves the town of Ladysmith in Natal, which has been besieged by a Boer force since 30 October 1899.
6 March 1900	Germany [births and deaths]	Gottlieb Daimler, German mechanical engineer who built one of the first successful cars powered by an internal combustion engine, dies in Cannstatt, Germany (65).
25 April 1900	Austria [births and deaths]	Wolfgang Pauli, Austrian-born US physicist, who discovers the principle that no two electrons in the same atom can have the same energy, born in Vienna, Austria (–1958).
17 May - 18 May 1900	South Africa [Anglo–Boer Wars (1899–1902)]	British forces under General Sir Redvers Buller relieve the town of Mafeking, southern Africa, following a seven-month siege by a Boer force.
13 June 1900	China [revolution]	The Boxer Rebellion by supporters of the Society of Harmonious Fists begins in China, in opposition to the growth of European influence there.
2 July 1900	Germany [aircraft]	German inventor Ferdinand Graf von Zeppelin's lighter-than-air ship LZ-3D1 makes its first flight, at Lake Constance, Germany. It has an aluminium sheeting hull.
4 July 1900	USA [births and deaths]	Louis Armstrong, US jazz trumpeter, composer, and band leader, born in New Orleans, Louisiana (–1971).
8 August - 10 August 1900	USA, UK [tennis]	The US public official Dwight Filley Davis presents an international challenge cup for lawn tennis, the Davis Cup. The USA wins the trophy, beating Britain 3–0 at Brookline, Massachusetts.
25 August 1900	Germany [births and deaths]	Friedrich Nietzsche, German philosopher and critic, especially of Christianity, dies in Weimar, Thuringian States (55).
31 August 1900	UK [food and drink]	Coca-Cola goes on sale in Britain.
7 October 1900	Germany [births and deaths]	Heinrich Himmler, German Nazi leader, head of the SS, and organizer of the Nazi death camps, born in Munich, Germany (–1945).
16 October 1900	UK [elections]	In the ‘khaki’ election in Great Britain, the Conservatives, successful in the Second Anglo-Boer War, remain in power with a majority of 134. The Conservatives and Unionists take 334 seats, the Liberal Unionists 68, the Liberals 184, the Irish Nationalists 82, and Labour 2. Prime Minister Lord Salisbury reconstructs his government, appointing Lord Lansdowne as foreign secretary.
17 October 1900	Germany [administration]	Bernhard von Bülow succeeds the aged Prince Chlodwig von Hohenlohe as the German chancellor.
6 November 1900	USA [elections]	In the US presidential elections, the Republican candidate William McKinley is re-elected as president of the USA. In the Congressional elections, the Republicans retain majorities in the House (197–151) and Senate (55–31).
11 November 1900	South Africa [Anglo–Boer Wars (1899–1902)]	Following British conquests, the Boer forces under General Christiaan De Wet resort to guerrilla tactics, raiding communications and British outposts. Horatio, Lord Kitchener orders that women and children related to Boer combatants be interred in concentration camps, and extends the ‘scorched earth’ policy started by Field Marshal Frederick, Lord Roberts, destroying Boer farms.
22 November 1900	England [births and deaths]	Arthur Seymour Sullivan, British composer of operettas with William Schwenk Gilbert, dies in London, England (58).
30 November 1900	Ireland, France [births and deaths]	Oscar Wilde, Irish poet and dramatist, dies in Paris, France (44).