This is a timeline of the 20th century.
- 1901: First Nobel Prizes awarded. The Australian colonies federated. Boxer Rebellion ends. Edward VII becomes King of the United Kingdom and the British Dominions and Emperor of India upon the death of Queen Victoria. Platt Amendment limits the autonomy of Cuba in exchange for withdrawal of American troops. Assassination of William McKinley. Emily Hobhouse reports on the terrible conditions in the 45 British concentration camps for Boer women and children in South Africa. Guglielmo Marconi receives the first trans-Atlantic radio signal.
- 1902: Second Boer War ends. Philippine–American War ends. Cuba gains independence from the United States. Willis Carrier invents the first modern electrical air conditioning unit. Unification of Saudi Arabia begins. Venezuela Crisis, in which Britain, Germany and Italy sustain a naval blockade on Venezuela in order to enforce collection of outstanding financial claims.
- 1903: First controlled heavier-than-air flight of the Wright Brothers. Herero and Namaqua Genocide, the first genocide of the 20th century, begins in German South-West Africa. In Russia the Bolsheviks and the Mensheviks form from the breakup of the Russian Social Democratic Labor Party. Pius X becomes Pope. The teddy bear is invented. The first Tour de France is held. Independence of Panama, the Hay–Bunau-Varilla Treaty is signed by the United States and Panama. The Ottoman Empire and the German Empire sign an agreement to build the Constantinople-Baghdad Railway.
- 1904: Entente cordiale signed between Britain and France. A Japanese surprise attack on Port Arthur (Lushun) starts the Russo-Japanese War. Trans-Siberian railway is completed. Construction of the Panama Canal begins. Roger Casement publishes his account of Belgian atrocities in the Congo Free State. End of British expedition to Tibet.
- 1905: Russo-Japanese War ends. Revolution of 1905 in Russia. Persian Constitutional Revolution begins. Trans-Siberian Railway opened. Albert Einstein's formulation of relativity. Schlieffen Plan proposed. The British Indian Province of Bengal, was partitioned by the Viceroy of India, Lord Curzon. First Moroccan Crisis. The Norwegian Parliament declares the union with Sweden dissolved, and Norway achieves full independence.
- 1906: Earthquakes in San Francisco, California (death toll: 3000) and Valparaíso, Chile (death toll: 20,000) occur. Dreyfus Affair ends. Stolypin reform in Russia creates a new class of affluent kulaks. Brazilian inventor Alberto Santos-Dumont takes off and flies his 14-bis to a crowd in Paris. The Muslim League is formed by Nawab Salimullah Khan of Dacca. The US began the Second Occupation of Cuba.
- 1907: Herero and Namaqua Genocide ends. A peasants' revolt in Romania kills roughly 11,000. The Indian National Congress splits into two factions at its Surat session, presided by Rash Behari Bose. Persian Constitutional Revolution ends with the establishment of a parliament. Japan–Korea Treaty of 1907. The Anglo-Russian Entente bring a pause in The Great Game in Central Asia. Elections to the new Parliament of Finland are the first in the world with woman candidates, as well as the first elections in Europe where universal suffrage is applied.
- 1908: First commercial radio transmissions. The Ford Motor Company invents the Model T. First commercial Middle-Eastern oilfield established, at Masjed Soleyman in southwest Persia. The Tunguska impact devastates thousands of square kilometres of Siberia. Young Turk Revolution in the Ottoman Empire. Independence of Bulgaria. Austro-Hungary annexes Bosnia-Herzegovina, triggering the Bosnian Crisis. Pu Yi, the last Emperor of China, assumes the throne. 1908 Messina earthquake kills over 70,000 people. Start of publication of Robert Baden-Powell's Scouting for Boys in London.
- 1909: United States troops leave Cuba. Bosnian crisis ends with Austro-Hungary's annexation of Bosnia and Herzegovina. Robert E. Peary claims to have reached the North Pole though the claim is subsequently heavily contested. Anglo-Siamese Treaty of 1909. Ottoman countercoup fails in the Ottoman Empire. A revolution forces Mohammad Ali Shah, Persian Shah of the Qajar dynasty to abdicate in favor of his son Ahmad Shah Qajar. Japan and China sign the Jiandao/Gando Treaty