The outcome of World War I hit Flensburg hard. After a referendum, the present border was fixed in 1920. North Schleswig became part of Denmark and Flensburg, a border town. Fewer bombs fell on Flensburg than on comparable cities during World War II so that Flensburg remained practically intact. However the refugee situation after the war and later was terrible. The final government fled as far as here and had it´s last seat in Flensburg. The government under Großadmiral Dönitz declared the capitulation and the end of the Third Reich from the Naval College in Mürwik on 7th May 1945.
Tabellarische Darstellung:
| 1900 | • The foundation of the Trade Corporation. • Population at the census of 1.12: 48,922. |
| 1903 | • Arts and crafts museum opened. |
| 1904 | • Setting up of professional fire-brigade. |
| 1907 | • Tram lines switched to electricity. • The Flensburg Wharf with 42,504 BRT delivered tonnage heads the German wharf industry, directly followed by Blohm and Voss (42,110 BRT), Stettiner Vulkan (42,105 BRT). |
| 1910 | • The Mürwik Naval College is opened. • Flensburg has by far the greatest number of shipping companies after Hamburg and Bremen. |
| 1911 | • Inauguration of the ‘Friedenshügel’ cemetery. |
| 1912 | • Construction of a new electricity plant. |
| 1914-1918 | • First World war. |
| 1918 | • Germany becomes Republic. |
| 1919-1920 | • Referendum in Dukedom of Schleswig. The first zone (North Schleswig) votes in an en-bloc election for Denmark, which receives 75% of the vote. On 14th March there is an election commune by commune in the second zone and in Flensburg. Flensburg decides with 75% of the vote to remain in Germany. The new border is drawn 5 km north of Flensburg. The economic consequences are serious. Flensburg loses almost half its sales area. The loss in turnover in Flensburg is on average about 30%. The town stagnates in the following years. • The mill-stream is covered over. Written language: High German. • Spoken language: High German, Low German. |
| 1922 | • Opening of the first sewage plant on the Lautrup brook (until 1963). |
| 1923 | • Opening of the free harbour (closed 1935). |
| 1925 | • Opening of the Schäferhaus airport. |
| 1926 | • Opening of the 'Seegrenzschlachthofs' (until 1973). |
| 1927 | • The inauguration of the stadium at Kielsenger Feld. • Opening of the modern railway station. |
| 1928 | • Radio mast put into operation. |
| 1929 | • Beginning of the world recession. Flensburg is badly affected due to its economic weakness. In 1930 an increasing number of ships lie at anchor in the harbour. The Flensburg Shipbuilding Company (FSG) ceases to operate (until 1934). In 1930 there are 6,000 unemployed. The town’s welfare costs increase six-fold in comparison with 1913. In the same year the number of oaths of disclosure increases three-fold in comparison with 1924. The paper –processing plant closes temporarily. The number of unemployed reaches about 9,000. |
| 1930 | • Opening of the ‘Deutsches Haus’. |
| 1931 | • The central bus station – the first of its kind on Germany – is put into operation. |
| 1933 | • The Nazis seize power, beginning of the Nazi dictatorship. • Boycott of Jewish shops, burning of books on the ‘’Exe'. • The Horn and the Schuldt shipping companies move to Hamburg. |
| 1935 | • Renewal of a large part of the harbour bulwark. |
| 1935-1937 | • Founding of a Torpedo and Communications College in Flensburg-Mürwik (today: the Naval base and Telecommunications College). |
| 1936 | • Construction of the tank barracks (Meiereistraße) |
| 1938 | • Building of the barracks on the Danish border. • The crematorium is put into operation. • The destruction of the Jägerslust estate belonging to the Wolff family in the pogrom night of 9-10.11.1938. |
| 1939 | • Census. The population reaches 70,871. |
| 1939-1945 | • Second World war. |
| 1945 | • In May Flensburg and the ‘restricted area’ Mürwik round the Naval College is the refuge for several thousand members of the party, state and army. • Occupation by Allied troops. Severe explosion at the harbour with 60 dead in June (after the end of the war). |
