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.
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. 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.
1923 — the city of Tangier becomes an International Free Zone after France and Spain end their control over parts of the city.
1924 — 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.
1925 — 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.
1934 — The borders of Libya are changed to their present-day boundaries after the Italo-British-Egyptian Agreement, British Sudan cedes northern territory to Libya.
World War II — 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.
1953, August 1 — Federation of Rhodesia and Nyasaland established from the British self-governing colony of Southern Rhodesia and the British protectorates of Northern Rhodesia, and Nyasaland.
1961, May 31 — 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)
1967, May 30 — 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.
2024, April 1 — Puntland announces its independence from Somalia among constitutional disputes and internal issues. It has no other formal recognition.
World War II — In the early stages of World War II in the Pacific, Japan made steady gains against the Allies. In 1940, with the collapse of France in Europe, the new Vichy regime allows Japan to annex French Indochina. After the attack on Pearl Harbor, Japan proceeds to occupy Wake Island, the Philippines, British Malaya, the Dutch East Indies, northern New Guinea and a number of pacific islands. Also Japan begins attacks against British-held Burma and India, and creates a puppet regime in Burma. From 1943 to its defeat, Japan steadily loses territory in the Pacific to the Allies and in 1945, Japan surrenders, abolishing its remaining puppet regimes in Manchukuo and Mengjiang, and abandoning its hold on Korea.
1945 — Following the war, the Soviet Union annexes the Southern Sakhalin and Kuril Islands from Japan according to the Yalta Conference, and Korea is divided into the two countries, South Korea and North Korea.
1948 — The State of Israel is created after the 1947 United Nations General AssemblyResolution 181 called for the partition of the British-ruled Palestine into a Jewish state and an Arab state. The resolution is accepted by the Jews in Palestine, but rejected by the Arabs in Palestine and the Arab states.
1955 — The Soviet Union hands over Dalian port to the People's Republic of China.
1960 — Cyprus declares its independence from the United Kingdom; the Sovereign Base Areas of Akrotiri and Dhekelia are established on the island by the United Kingdom under the latter's control.
1961, December 19 — India takes over the Portuguese colony of Goa, Daman and Diu, which becomes a single Union Territory of India. In 1987, Goa is elevated to full statehood, with Daman and Diu remaining a Union Territory.
1962, August 16 — India officially absorbs the French enclaves of Pondicherry.
2005, August — Israel dismantles its settlements in the Gush Katif region of the Gaza Strip, and the remainder of the Gaza Strip, most of which had already been transferred to Palestinian rule in 1994, becomes administered by the Palestinian Authority, until 2007 when the territory is seized by the military wing of Hamas in a violent coup d'état.
2005 — Israel dismantles its settlements in the Northern Samaria region of the West Bank.
2020 — While Nagorno-Karabakh remained an internationally recognised territory of Azerbaijan, the four UN Security Council resolutions, adopted in 1993 and demanding immediate withdrawal of the Armenian occupying forces from all occupied regions of Azerbaijan, remained unfulfilled until 2020. In 2020, a new war erupted in the region, which saw Azerbaijan retake control of most of southern Karabakh (Fuzuli, Jabrayil, Zangilan, Qubadli, Hadrut districts) and parts of north-eastern Karabakh (Talish, Madagiz). A trilateral ceasefire agreement signed on 10 November 2020, ended the war and forced Armenia to return control of all of the remaining territories surrounding Nagorno-Karabakh.
1921 — As a result of winning a war against Soviet Russia, Poland gains territories east of the Curzon Line, inhabited essentially by Lithuanians, Belarusians, Poles, and Ukrainians.
1923 — The Treaty of Sèvres is superseded by the Treaty of Lausanne under which Greece loses its earlier territorial gains and the borders of modern Turkey are established. Western Thrace is ceded by Bulgaria to Greece, a decision earlier agreed upon in the 1919 Treaty of Neuilly-sur-Seine. On the Baltic sea, Lithuania annexes the Memel territory without plebiscite. Italian military forces take control of the Greek island of Corfu.
1924 — The Treaty of Rome is concluded on January 27, ending the existence of the Free State of Fiume and the Italo–Yugoslav border dispute. The treaty assigns Fiume (Rijeka) to Italy and Sušak to Yugoslavia, with joint port administration. On March 16, Italy formally annexes Fiume.
1926 — Albania cedes territory to the Kingdom of Slovenes, Croats and Serbs.
1930 — Bouvet Island is located in the Subantarctic, and declared a Norwegian dependency after a dispute with the United Kingdom.
1934 — Erik the Red's Land, located in the east of Greenland, is returned to Denmark. The area had been occupied by Norway since 1931, but Norway accepted that the Permanent Court of International Justice ruled against this.
1935 — Saarland is annexed by Nazi Germany after a plebiscite is held.
1938 — Austria is annexed by Nazi Germany in the Anschluss. The United Kingdom returns the Treaty Ports to Ireland as part of the Anglo-Irish Trade Agreement over several months during the year. The Munich Agreement on September 29 permits Germany to also annex the Sudetenland region of Czechoslovakia. The First Vienna Award on November 2 awards southern Slovakia and southern Subcarpathian Rus' from Czechoslovakia to Hungary, while Poland independently annexes Zaolzie (Těšín) shortly after.
1939 — The Memel territory is ceded to Nazi Germany by Lithuania under pressure from Berlin on March 23. The rest of the Czech lands is taken over by Nazi Germany: a German protectorate called Bohemia and Moravia is formed on the remaining Czech lands shortly after the proclamation of the Slovak Republic. The same day, Hungary occupies and annexes the remainder of Carpathian Ruthenia and by the Slovak–Hungarian War acquires further territories from Slovakia. On August 23, the Molotov–Ribbentrop Pact is signed. Nazi Germany invades Poland on September 1; the Soviet Union - on September 17, regaining territories lost in 1921 in the Polish–Soviet War, and a bit more.
World War II — Many boundary changes occur during the Second World War as Axis powers and the Soviet Union re-divide the areas under their control.
1945 — Following the war, the borders of Germany are moved west to the Oder-Neisse line, while the approximate boundary of the Curzon Line is used as the eastern border of Poland. In addition to incorporating the Kresy territories, the Soviet Union also annexed the Baltic states, Carpathian Ruthenia from Czechoslovakia, and Bessarabia, the Hertsa region, and Northern Bukovina from Romania. From Germany, the Soviet Union acquired the northeastern third of the former East Prussian exclave with the Klaipeda/Memel region becoming part of the Lithuanian SSR and the bulk of the territory forming the Kaliningrad Oblast of the Russian SFSR. Additionally, Finland ceded major portions of Karelia and Salla to the Soviet Union as well as islands in the Gulf of Finland, the whole Petsamo, and a lease to use Porkkala as a Soviet naval base for 50 years.
1948 — Following the signal of the Moscow Protocol of 1948, the Soviet Union formally annexes some Danubian islands and the Snake Island in the Black Sea from Romania.
1955, April 23 — Italy and Switzerland modify the border in the zone of Lago di Lei
1955, July 27 — The Austrian State Treaty comes into force, establishing an independent Austrian state from the four occupation zones of the Allied powers.
1961 — An adjustment to the Meuse river between The Netherlands and Belgium results in three small packages of land being exchanged between the two countries.
1963 — The 1949 Dutch acquisitions of West German territory are almost completely reverted; the Duivelsberg remains permanently with the Netherlands.
1990 — East Germany unites with West Germany on October 3. Transnistria declares independence from the Moldavian SSR but is not recognised by any country.
2016, November 28 — Belgium and the Netherlands swap land near Lanaye and Oost-Maarland over the discovery of a headless body several years prior, which the Belgian authorities could not access without crossing Dutch territory. The border has been straightened out and now runs down the centre of the Meuse River. The change took effect on 1 January 2018.
2022, September 30 — Russia unilaterally declares the annexation of the Ukrainian oblasts of Luhansk, Donetsk, Zaporizhzhia, and Kherson. Similar to the annexation of Crimea in 2014, this border change is not recognised internationally.
North America
1927, April 1 — The Imperial Privy Council of the United Kingdom establishes the boundaries of the Dominion of Newfoundland and Canada, in particular, the province of Quebec, which affirmed that territories claimed by Quebec were part of Newfoundland. Previous maps showed the disputed territory as undefined.
1949, March 31 — The Dominion of Newfoundland joins Canada. The territory is now called Newfoundland and Labrador.
1962, August 6 — Jamaica gains independence from the United Kingdom.
1962, August 31 — Trinidad and Tobago gains independence from the United Kingdom.
1966, November 30 — Barbados gains independence from the United Kingdom.
1973, July 10 — The Commonwealth of The Bahamas gains independence from the United Kingdom.
1974, February 7 — Grenada gains independence from the United Kingdom.
1999 — Panama Canal Zone returns from joint US–Panamanian control to Panamanian control. A previous important development was the 1979 change from US control to joint US–Panama control, with plans for full Panamanian sovereignty at some point after that.
1949, July — The Territory of New Guinea joins with the Australian Territory of Papua to form The Territory of Papua and New Guinea. The union is an administrative one only and does not affect the separate position of the Territory of New Guinea as a territory governed by Australia as a United Nations trust territory.
1974 — A referendum is held in the British colony of the Gilbert and Ellice Islands. Per the results of the referendum, the colony was divided into two.
1975, September 16 — The Territory of New Guinea and the Territory of Papua which were in an administrative union under Australian governance with the name Papua New Guinea are unified as a single sovereign country called the Independent State of Papua New Guinea.
1979 — The Marshall Islands leaves the Trust Territory of the Pacific Islands, becomes an independent country while also an associated state with the U.S.
1979 — The Federated States of Micronesia formed from part of the Trust Territory of the Pacific, also independent as an associated state with the U.S.
1994 — The Republic of Palau is formed from the remainder of the Trust Territory of the Pacific, as an independent state associated with the U.S.
South America
1938 — A ceasefire signed between Paraguay and Bolivia awards Paraguay three-quarters of the Chaco Boreal which it took over during the Chaco War (1932–35).
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