Since World War I, there have been many changes in borders between nations, detailed below. For information on border changes from the end of the Napoleonic Wars to 1914, see the list of national border changes (1815–1914). Cases are only listed where there have been changes in borders, not necessarily including changes in ownership of a territory. For instance, many European colonies in Africa became independent without any adjustment to their borders, although some did have many changes. Also mentioned are some de facto changes, not recognized by the international community, such as Crimea, and South Ossetia.
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, the borders of Africa, and 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. As a result of New Imperialism, the European countries with the most colonies throughout history were: the United Kingdom (115), France (53), Portugal (52), Spain (44), the Netherlands (29), Germany (20), Russia (17), Denmark (9), Sweden (8), Italy (7), Norway (6), Belgium (3) and Greece (1).
Africa 1919–1922 — The Treaty of Versailles divides Germany's African colonies into mandates of the victors (which largely become new colonies of the victors). Most of Cameroon becomes a French mandate with a small portion taken by the British and some territory incorporated into France's previously existing colonies; Togo is mostly taken by the British, though the French gain a slim portion; German East Africa was separated between Belgium (Rwanda and Burundi), Portugal (the Kionga Triangle) and the United Kingdom (Tanganyika, later merging with Zanzibar to form Tanzania); and German South-West Africa (Namibia) becomes a mandate of South Africa. In September, France settles its African colonial borders with Italian Libya. On September 8, following the signing of the Anglo-French Convention of September 8, 1919, the borders of Italian Libya and French Chad are settled to the present-day boundaries., United States Department of State, October 16, 1961 A few days later, the borders of western and southwestern Libya are extended to their current boundaries after French concessions with the Franco-Italian Arrangement of 12 September 1919., United States Department of State, April 28, 1961 — The UK cedes a portion of Jubaland to Italy (Trans-Juba, it. Oltregiuba) as a reward for the Italians having joined the Allies in World War I. — The Tangier International Zone is established after France and Spain end their control over parts of the city. — The eastern borders of Libya and British Egypt are changed to their present boundaries, with the exception of parts of present-day southern Libya still remaining part of British Sudan. — France moves the control of the area of the present day Borkou-Ennedi-Tibesti Prefecture from the territory of Niger in French West Africa to Chad in French Equatorial Africa., United States Department of State, December 15, 1978 — The borders of Libya are changed to their present-day boundaries after the Italo-British-Egyptian Agreement, British Sudan cedes northern territory to Libya. — The Franco-Italian Agreement cedes the Aouzou Strip from French Chad to Italian Libya. — After the success of Italy during the Second Italo-Abyssinian War, Ethiopia is annexed by Italy. Ethiopia joins with Eritrea and Italian Somaliland to form Italian East Africa. The international community does not accept Italy's occupation of Ethiopia and maintains relations with exiled Ethiopian Emperor Haile Selassie. 1940 – 1943 — With the outbreak of World War II, war arrives in Africa in 1940, with Italy joining the war, initially British forces in British Somaliland are defeated by the Italians coming from Italian East Africa and the territory is taken. However, by 1941, the British retake lost territory and take over Italian East Africa. In North Africa, after a period of retreat into Libya, Italian forces receive vital aid from the German army and the Germans move deep into Egypt by 1942, before beginning to lose ground. By 1943, The German and Italian forces retreat from Libya and capture Tunisia from France prior to fleeing to Sicily. — The Prince Edward Islands are annexed by the Union of South Africa. — The Kingdom of Libya becomes independent. — British-administered Eritrea is joined into a federation with Ethiopia.
— Federation of Rhodesia and Nyasaland established from the British self-governing colony of Southern Rhodesia and the British protectorates of Northern Rhodesia, and Nyasaland. — Sudan gains independence. — Tunisia gains independence. — French Morocco, the International Zone of Tangier, and the northern zone of Spanish Morocco join to become the independent nation of Morocco. — The United Kingdom annexes British Togoland and the Northern Territories protectorate as part of Her Majesty's dominions in Ghana, a new independent country within the British Commonwealth. — French West Africa splits into Mauritania, Senegal, French Sudan (now Mali), French Guinea (now Guinea), Côte d'Ivoire, Niger, Upper Volta (now Burkina Faso) and Dahomey (now Benin) — With the Treaty of Angra de Cintra, Spain relinquishes its protectorate in the Southern Zone (Cape Juby) of Spanish Morocco, which joins the independent nation of Morocco. Much (though not all) of the area of the Territory of Ifni is effectively ceded by Spain as well. — Belgian Congo is granted independence as the Republic of the Congo. In 1964 it changes its name to the Democratic Republic of the Congo to differentiate itself from Congo-Brazzaville. — State of Somaliland (formerly British Somaliland) joins with Italian Somaliland to form Somalia. French Equatorial Africa's interim successor, the Union of Central African Republics dissolves in August with independence of Chad (August 11), Oubangui-Chari (now Central African Republic) (August 13), Congo-Brazzaville (now the Republic of the Congo) (August 15), and Gabon (August 17). — the northern two-thirds of British Cameroons joins Nigeria; October 1 — the southern third of British Cameroons joins with the Republic of Cameroon to form the Federal Republic of Cameroon. This year also the tiny Portuguese outpost of São João Baptista de Ajudá was annexed by Dahomey (now Benin) — The Belgian colony of Ruanda-Urundi separated into Rwanda and Burundi. — The People's Democratic Republic of Algeria is formally officially regained its sovereignty. — Federation of Rhodesia and Nyasaland dissolved; over the next two years Nyasaland becomes independent Malawi, Northern Rhodesia wins independence as Zambia, and Southern Rhodesia (or simply Rhodesia) unilaterally declares independence. — Tanganyika unites with the island of Zanzibar to form Tanzania. Bechuanaland becomes an independent Commonwealth republic as Botswana. The British colony of Basutoland becomes an independent state of Lesotho. — The break-away state of Biafra is formed from southern Nigeria. Officially Biafra receives de jure acknowledgement of existence by only a few nations, but has the de facto support of France, Israel, Portugal, and South Africa which provide arms to the state in its war of independence against Nigeria. - Eswatini, Britain's last African colony gains independence. — Spain returns Ifni to Morocco. — Biafra is occupied and annexed by Nigeria. — The Portuguese Overseas Province of Guinea declares its independence as the Republic of Guinea-Bissau. Recognition is granted the next year on 10 September 1974. — The Portuguese Province of Mozambique gains independence as the People's Republic of Mozambique. — The Portuguese Overseas Province of Cape Verde gains independence as the Republic of Cape Verde. — The French State of the Comoros gains independence as the State of Comoros. — The Portuguese Overseas Province of São Tomé and Príncipe gains independence as the Democratic Republic of São Tomé and Príncipe. — The Portuguese State of Angola gains independence as the People's Republic of Angola. — Spanish Sahara divided de facto between Morocco and Mauritania (although Spain's formal mandate did not end until February 26, 1976). Western Sahara is de jure a non-self governing territory according to the UN. No country recognised this until 2020, when the United States recognised Morocco's annexation. — The British Crown Colony of the Seychelles gains independence as the Republic of Seychelles. — The French Territory of the Afars and the Issas gains independence as the Republic of Djibouti — South African Government reimposed direct rule on Walvis Bay. — Mauritania withdraws from southern Western Sahara, which is taken over by Morocco — Namibia gets independence from occupying South Africa. — Somaliland declares independence from Somalia but is not recognized by any other country. — Eritrea breaks off from Ethiopia. — Walvis Bay and the Penguin Islands are transferred by South Africa to Namibia. — Bakassi transferred to Cameroon by Nigeria — South Sudan formally obtains independence from the Republic of Sudan. — Puntland announces its temporary independence from Somalia until constitutional disputes and internal issues are to be resolved. It has no other formal recognition. — The ICJ resolves the territorial dispute between Gabon and Equatorial Guinea, awarding the latter country the Islands of Mbanie, Cocotier, and Conga.
Asia — The German Concession in Shandong is formally transferred to Japan as part of the Treaty of Versailles. It had been under de facto Japanese control since the 1914 Siege of Tsingtao. — Xu Shuzheng, Chinese warlord of the Republic of China, invades Outer Mongolia, repelling the White Army and reintegrating Mongolia into China. — The White Army defeat the Chinese Forces, ending the Occupation of Mongolia by the Beiyang government and re-establishing the Bogd Khanate. — The Tuvan People's Republic is proclaimed by revolutionaries with support from the Bolsheviks. — Japan agrees to transfer its lease in Shandong to China during the Washington Naval Conference, resolving the Shandong Problem. — The Saudi Arabian–Iraqi neutral zone is created. — The Mongolian People's Republic is established in the first constitution following the defeat of White Forces in the region and the end of the Russian Civil War. December — The Sultanate of Nejd annexes the Kingdom of Hejaz and subsequently decrees the Kingdom of Hejaz and Nejd in 1926. — The Treaty of Ankara is signed, recognising the Iraq-Turkey border with some minor modifications and solving the Mosul question. — The ICJ awards the Island of Palmas from the Philippines to the Dutch East Indies. — The Soviet Union seizes the Bolshoy Ussuriysky Island from the Republic of China. — The Empire of Japan declares Manchukuo independent of China — The Kingdom of Hejaz and Nejd annexes the Idrisid Emirate of Asir and subsequently establishes the Kingdom of Saudi Arabia. — Japan declares Mengjiang independent of China. — The British split Burma and Aden off from the rest of the Raj — Hatay State, a city-state, is formed when it separates from French-held Syria. — Turkey annexes Hatay.