This is a timeline of geopolitical changes around the world between 1900 and 1999. It includes dates of declarations of independence, changes in country name, changes of capital city or name, and changes in territory such as the annexation, cession, concession, occupation, or secession of land. Territorial conquests as a result of war are included on the timeline at the conclusion of military campaigns, but changes in the course of specific battles and day-to-day operations are generally not included. Changes in airspace and maritime territory are included only when they are subject to a dispute. Over 50% of the world's borders today were drawn as a result of British and French imperialism. The British and French drew the modern borders of the Middle East, 80% of the borders of Africa, in Asia after the independence of the British Raj and French Indochina and the borders of Europe after World War I as victors, as a result of the Paris treaties.Lovejoy, Paul E. (2012). Transformations of Slavery: A History of Slavery in Africa. London: Cambridge University Press.Martin Klein, "Slave Descent and Social Status in Sahara and Sudan", in Reconfiguring Slavery: West African Trajectories, ed. Benedetta Rossi (Liverpool: Liverpool University Press, 2009), 29.
1900s
YearDateEvent1900 1 JanuaryThe Northern Nigeria Protectorate and Southern Nigeria Protectorate are established by the United Kingdom.16 FebruaryThe United States of America takes control of American Samoa under the terms of the Tripartite Convention.MarchThe First Republic of Acre capitulates and is reabsorbed by the Republic of Bolivia. 21 AprilThe United Kingdom annexes the island of Niue, making it a British protectorate.28 MayThe United Kingdom occupies the Orange Free State.5 SeptemberThe colony of French Chad is established. Fort-Lamy is the capital.NovemberAcre declares independence from Bolivia as the Second Republic of Acre. The movement is quickly suppressed and Acre remains part of Bolivia. The border between the Republic of the United States of Brazil and the French colony of Guyane (French Guiana) is defined by arbitration. The French troops that advanced to the margins of the Araguari River repair to the Oiapoque River.19011 JanuaryThe Commonwealth of Australia is established by federation of the British colonies of New South Wales, Victoria, Queensland, South Australia, Western Australia and Tasmania. Melbourne was the de facto (but not de jure) seat of government from 1901 to 1927.23 MarchThe First Philippine Republic dissolves.11 JuneThe United Kingdom transfers the Cook Islands and Niue to the Colony of New Zealand.26 SeptemberThe United Kingdom occupies the Ashanti Empire and makes it a Crown colony.HL Deb 16 January 1902 vol 101 c57’The Map of Africa by Treaty’ by Sir E. Hertslet pg. 77190218 MarchThe Crown colony of British New Guinea is transferred from the United Kingdom to Australia, which reorganizes it as the Territory of Papua.20 MayThe Republic of Cuba gains independence from the United States of America. Havana is the capital.31 MayThe United Kingdom creates the Orange River Colony from the Orange Free State and the Transvaal Colony from the South African Republic (Republic of Transvaal). Bloemfontein and Pretoria remains the respective capitals.1 JulyThe United Kingdom annexes Henderson Island.10 JulyThe United Kingdom annexes Oeno Island.20 NovemberKing Edward VII of Britain adjusts borders in the Cordillera of the Andes Boundary Case between Chile and Argentina.19 DecemberThe United Kingdom annexes Ducie Island. The Zaria Emirate and the Abuja Emirate are annexed into the British Northern Nigeria Protectorate. German Kamerun annexes the Mandara Kingdom.190327 JanuaryThe Third Republic of Acre declares its independence from Bolivia. The capital is Cidade do Acre.23 FebruaryCuba leases Guantanamo Bay to the United States of America in perpetuity.12 MayMauritania becomes a protectorate of the French Republic. Saint-Louis is the capital.29 JulyThe Adamawa Emirate is annexed into the British Northern Nigeria Protectorate and German Kamerun.20 OctoberThe Alaska boundary dispute is resolved between the United States of America and Canada.3 NovemberThe Republic of Panama secedes from the Republic of Colombia. Panama City is the capital.11 NovemberThe Republic of Bolivia and the Republic of the United States of Brazil sign the Treaty of Petrópolis. Bolivia receives land in Mato Grosso from Brazil, and Brazil absorbs the Republic of Acre.18 NovemberThe new Republic of Panama grants the United States of America control of the Panama Canal Zone. Balboa is the administrative center. The United Kingdom secedes the Seychelles from the colony of Mauritius. After the Aceh War, the Sultanate of Aceh is annexed by the Kingdom of the Netherlands and becomes part of the Dutch East Indies.190413 FebruaryFollowing the Franco-Siamese Convention, the Kingdom of Siam concedes border territories to French Indochina in exchange for French-occupied Chantaburi.4 MayThe United States of America annexed the Panama Canal Zone.4 OctoberThe Franco-Spanish Convention of Paris acknowledges formal control of Saguia el-Hamra (later northern Spanish Sahara) by the Kingdom of Spain. The border between the Republic of the United States of Brazil and British Guiana is defined by arbitration. Approximately half of the disputed land goes to each side. French Dahomey is established. Porto-Novo is the capital. The Kingdom of Champasak is annexed by France and becomes part of the French protectorate of Laos.19057 JuneThe Kingdom of Norway declares its independence from the United Kingdoms of Sweden and Norway through dissolution of the personal union with Kingdom of Sweden.5 SeptemberThe Liaodong Peninsula and the Russian railway in south Manchuria are leased to the Empire of Japan following the Treaty of Portsmouth.The Empire of Japan annexes Sakhalin Island south of 50° N following the Treaty of Portsmouth.26 OctoberThe Kingdom of Sweden recognizes the union dissolution and the independence of Kingdom of Norway. The United Kingdom moves the capital of the East Africa Protectorate from Mombasa to Nairobi.1906 1 May The British Colony of Lagos and the Southern Nigeria Protectorate merge to form the Colony and Protectorate of Southern Nigeria. The French Republic divides its colony of French Congo into the colonies of Gabon and Middle Congo. Libreville remains the capital of Gabon. Brazzaville becomes the capital of Middle Congo. The United Kingdom and France jointly administer the New Hebrides. Port Vila is the capital.190723 MarchThe Kingdom of Siam concedes territory to French Indochina in exchange for Trat.24 AprilThe border between the Republic of the United States of Brazil and the Republic of Colombia is defined by the Bogotá Treaty. Brazil gains lands on the margins of the Solimoes River at the area known as Cabeça de Cachorro ("The Dog's Head").6 JulyThe British Central Africa Protectorate is renamed to Nyasaland Protectorate.26 SeptemberNew Zealand becomes a Dominion within the British Empire under the name Dominion of New Zealand. Wellington is the capital. The Dominion of Newfoundland is also declared the same day. St. John's is the capital.16 NovemberOklahoma is admitted to the Union as the 46th State of the United States.17 DecemberUgyen Wangchuck establishes the Kingdom of Bhutan. Punakha is the winter capital and Thimphu is the summer capital.19085 OctoberThe Kingdom of Bulgaria gains independence from the Ottoman Empire. Sofia is the capital.6 OctoberAustria-Hungary formally annexes the Ottoman Vilayet of Bosnia (under de facto Austro-Hungarian rule since the Treaty of Berlin 1878) as the Condominium of Bosnia and Herzegovina (causing the Bosnian crisis).15 NovemberKing Leopold II of Belgium sells his private Congo Free State to the Kingdom of Belgium. The colony is renamed the Belgian Congo.19099 JulyThe Kingdom of Siam transfers its southernmost provinces to British Malaya in the Anglo-Siamese Treaty of 1909.
1910s
YearDateEvent191015 JanuaryThe French Republic creates French Equatorial Africa from its colonies of Gabon, Middle Congo, and Oubangui-Chari. Libreville and Bangui yield to Brazzaville as the capital.29 March23 bancos are annexed by Mexico from the United States and 34 bancos are annexed by the United States of America from Mexico with the first application of the Banco Convention of 1905.31 MayThe Cape Colony, the Colony of Natal, the Transvaal, and the Orange River Colony unite as the Union of South Africa, which is established as a Dominion under the terms of the South Africa Act 1909.20 AugustCanada rescinds its claim to Pope's Folly Island in a treaty with the United States of America.Van Zandt, p. 2022 AugustThe Korean Empire capitulates and is annexed by the Empire of Japan.5 OctoberThe first Portuguese Republic supersedes the Kingdom of Portugal. The Kasanje Kingdom is annexed to Portuguese Angola.191117 AugustThe United Kingdom unites Barotziland–North-Western Rhodesia and North-Eastern Rhodesia to form Northern Rhodesia.4 NovemberIn the Morocco–Congo Treaty, Germany acquires the Neukamerun region from France in exchange for abandoning German claims in Morocco.29 DecemberThe Bogd Khanate of Mongolia declares independence from the Qing dynasty of China. Niislel Khüree is the capital. The capital of British India is moved from Calcutta to New Delhi.19121 JanuaryThe Republic of China overthrows the Qing dynasty of China in the Xinhai Revolution. Nanking is the provisional capital.6 JanuaryNew Mexico is admitted to the Union as the 47th State of the United States.14 FebruaryArizona is admitted to the Union as the 48th State of the United States.30 MarchThe Treaty of Fez formally re-establishes Morocco as a French Protectorate.7 NovemberMexico annexes 20 bancos from the United States and the United States of America annexes 11 bancos from Mexico.27 NovemberThe Treaty Between France and Spain Regarding Morocco assigns the northern and southern strips of Morocco to Spain.28 NovemberAlbania declares its independence from the Ottoman Empire. Tirana is the capital. The Wadai Empire is disestablished and annexed into French Chad.191313 FebruaryTibet declares independence from the Republic of China.MayThe Imamate of Oman rebels against the Sultanate of Muscat and Oman. Nizwa becomes the capital after it is conquered on 5 June.10 AugustFollowing the First Balkan War, the Treaty of Bucharest is signed, by the terms of which: Bulgaria gains Western Thrace and the southern portions of what are now Blagoevgrad Province and Burgas Province. Romania gains Southern Dobruja. Serbia gains Kosovo, most of what is now the Republic of Northern Macedonia, and some new land to the west of its previous borders. Greece gains Epirus, West Macedonia, Central Macedonia, and most of the islands in the Aegean Sea that it did not control before the war. Albania gains southern, eastern, and northern lands that bring it to its current borders. Albania becomes officially independent, though large portions of its lands remain disputed. Montenegro gains most of what is now its Northern Region.29 SeptemberFollowing the Second Balkan War, the Treaty of Constantinople is signed, by the terms of which: The Ottoman Empire regains the portions of Eastern Thrace it lost in the First Balkan War.