The Schleswig Plebiscites were two plebiscites, organized according to section XII, articles 109 to 114 of the Treaty of Versailles of June 28, 1919, in order to determine the future border between Denmark and Germany through the former duchy of Schleswig. The process was monitored by a commission with representatives from France, the United Kingdom, Norway and Sweden.
The Duchy of Schleswig was a fiefdom of the Danish crown, and was conquered by Prussia and Austria in the 1864 Second War of Schleswig along with the Danish-ruled German provinces of Holstein and Lauenburg, which had both been part of the Holy Roman Empire. Between 1864 and 1866, Prussia and Austria ruled the entire region as a condominium, and formalised this arrangement in the 1865 Gastein Convention. The condominium was terminated due to the Austro-Prussian War in 1866.
Article 5 of the Austro-Prussian Peace of Prague (1866) stipulated that a plebiscite should be held within 6 years to give the people of the northern part of Schleswig the possibility of voting for its future allegiance, allowing regions voting for Danish rule to be restored to Danish administration.
The idea of a plebiscite had been presented earlier. During the early phases of the First Schleswig War, the secessionist government of Schleswig-Holstein had unsuccessfully suggested a referendum in parts of Schleswig, but this had been rejected by the Danish government, and during the 1863 London Conference's attempts to defuse the Second Schleswig War, one of the suggestions of Prussian Prime Minister Otto von Bismarck was a referendum in North Schleswig. Bismarck's initiative was not adopted by the conference, primarily since the option had not been included in the instruction to the Danish delegation. The inclusion of the promise of a plebiscite in the 1866 Austro-Prussian Peace of Prague was a diplomatic concession to Austria, but was not implemented. The reference to it was subsequently dropped in the 1877 Treaty of Gastein between Austria and Germany. The 1864 border was confirmed in the 1907 German-Danish Optant Treaty, but Danish North Schleswigers continued to argue for a plebiscite citing the 1866 Peace of Prague.
Following the defeat of Germany in World War I, a request was made from the Danish government to the Allied Powers and the Versailles Conference for the inclusion of a plebiscite in the disputed North Schleswig region based on Woodrow Wilson's Fourteen Points as part of the Allied Powers' peace settlement with Germany, and this request was granted by the Allies.
The plebiscites were held on 10 February and 14 March 1920 in two zones that had been defined according to wishes by the Danish government, and based on lines drawn in the 1890s by Danish historian Hans Victor Clausen During the 1880s and 1890s, Clausen travelled extensively on both sides of the future border, and published two suggestions for a future Danish-German border. Clausen's first line delineated a coherent territory that he expected would vote Danish in a future referendum, and the second line (c. 10–20 km further south) including a thinly populated rural region in Central Schleswig, which Clausen believed had potential for assimilation into Denmark, as the population of Central Schleswig was pro-German in allegiance, but also Danish speaking.
In 1918, Clausen published a pamphlet "Før Afgørelsen" in which he strongly advocated Denmark to annex the zone delineated by his northernmost ("first") line, and argued that the territory north of this line was indisputably pro-Danish, and should be considered indivisible. At the same time, he effectively abandoned his second line, as the population of Central Schleswig remained pro-German, and as he considered it vital that the future border should be based on the self-determination of the local populace. In the 1920s referendum, Clausen's first line was closely imitated in what became the referendum's Zone I, while his second line became the basis of Zone II, although the referendum zone was extended to include the city of Flensburg and the town of Glücksburg. Clausen had excluded both from his two lines.
Zone I was based on Clausen's estimations of the local population's national self-identification. When in doubt, Clausen primarily relied on the wishes of the rural communities, which he considered autochtone, in contrast with the North Schleswig towns, which he considered largely irrelevant due to their smallness and their less autochtone population, notably the demographics of the town of Sønderborg (Sonderburg) which had become strongly influenced by the presence of a large German naval base. In addition, Clausen believed that it would minimize the risk of future conflict if the future border in the marshy West Schleswig followed either the Vidå river or a dyke. This caused resentment on the German side, as this implied that the town of Tønder (Tondern) would be included in zone I.
In 1918 and early 1919, the leading Danish political parties argued that the future allegiance of North Schleswig should be decided by a plebiscite, in which the entire region should be counted as one indivisible unit, i.e. vote en bloc. This wish was conveyed to the Paris Peace Conference in Versailles, and became the basis for the referendum's Zone I.
During 1919, political wishes in Denmark grew for the extension of the referendum area, and the issue became a topic of confrontation between the Social Liberal government supported by the Social Democrats, both of which opposed extending the area. The Liberal and Conservative opposition supported an extension of the referendum. As a compromise, it was decided to request the Allied Powers to extend the referendum until Clausen's second line, which was adapted to include Flensburg and Glücksburg. In this smaller Zone II, each parish was to decide its own allegiance. Two other requests were made, which were only partially followed by the Allied Powers. Firstly, Denmark requested that the referendum area's German civil administration be replaced by an international administration. The Allied Powers replaced the German garrisons with a small international force, but the civil administration was only partially replaced in Zone I, and not at all in Zone II. Secondly, Denmark had requested that persons previously expelled from the region should be allowed to vote in the referendum. This was intended to allow previously expelled "optants" to vote, i.e. the families of locals who in 1864 had selected to retain their Danish citizenship and who had consequently been expelled from the area by Prussian authorities. The Allied Powers granted this request but extended it, consequently entitling anyone who had previously lived in the region to vote in the referendum. Since a large number of German officials (notably railway officials) had been temporarily stationed in the area, this extension implied that these officials as well as their wives and any children of legal age were entitled to vote in the referendum. Since many of the expelled pro-Danish "optants" had emigrated to the United States, the net result of this extension was a slight increase for the German results.
On February 10, 1920, the plebiscite was held in Zone I, the later Northern Schleswig. There, 74.9% (75,431 votes) of the public voted to come under Danish rule, 25.1% (25,329 votes) to stay German, but in three of the four major towns, especially in the southern region directly at the frontier to Zone II German majorities existed, especially a large German majority between 70% and 80% in and around Tønder and Højer. It was mostly this area that caused controversy after the voting, especially as these towns had been included north of Clausen's first line. Although Clausen correctly estimated Tønder to be vastly pro-German, he considered the town to be economically dependent of its pro-Danish rural uplands, and assigned both the town and its uplands north of his first line.
The vote in Central Schleswig (Zone II) took place on March 14, 1920. 80.2% (51,742 votes) fell for Germany, 19.8% (12,800) for Denmark. Since a Danish majority in this zone was produced in only three small villages on the island of Föhr, none of which were aligned with the coming border, the Commission Internationale de Surveillance du Plébiscite au Slesvig decided on a line almost identical to the border between the two zones. The poor result for Denmark in Central Schleswig, particularly in Flensburg, Schleswig's largest city, triggered Denmark's 1920 Easter Crisis.
A plebiscite was not held in the southernmost third of the province (Zone III) as the population was almost exclusively pro-German, and the Danish government had expressly asked for this region not to be included in the referendum.
Selected results in detail:
|Electorate||German name||Danish name||For Germany||For Denmark|
|Zone I (Northern Schleswig), 10 February 1920||25.1 %||25,329||74.9 %||75,431|
|Town of||Sonderburg||Sønderborg||56.2%||2,601||43.8 %||2,029|
|Northern part of District of||Tondern||Tønder||40.9%||7,083||59.1%||10,223|
|Northern part of District of||Flensburg||Flensborg||40.6%||548||59.4%||802|
|Zone II (Central Schleswig), 14 March 1920||80.2 %||51,742||19.8 %||12,800|
|Southern part of District of||Tondern||Tønder||87.9%||17,283||12.1%||2,376|
|Southern part of District of||Flensburg||Flensborg||82.6%||6,688||17.4%||1,405|
|Northern part of District of||Husum||Husum||90.0%||672||10.0%||75|
Directly after the announcement of the results from Zone I, an alternative draft for the frontier was made by the German administrator Johannes Tiedje. The proposed frontier would have incorporated Tondern, Hoyer, Tingleff and neighbouring areas and also some parts north from Flensburg – the so-called Tiedje Belt – and would have created almost equal minorities on both sides of the frontier instead of 30,000 to 35,000 Germans in Denmark and 6,000 to 8,000 Danes in Germany.
Tiedje's Line was strongly criticised in Denmark, as it would have transferred a large number of pro-Danish communities south of the future border, and was refused by all parties in the Danish parliament. The referendum's entire Zone I was transferred to Denmark on 15 June 1920, and the territory was officially named the South Jutlandic districts, more commonly Southern Jutland, although the latter name name is also the historiographical name for the entire Schleswig region.
- Easter Crisis of 1920
- Schleswig-Holstein Question
- Danish minority in Southern Schleswig
- North Schleswig Germans
- History of Schleswig-Holstein
- Southern Schleswig
- Danish constitutional referendum, 1920
- Fredsforslag 1848, Peace Concept by the Government of Schleswig-Holstein 1848 (Danish)
- Myter om Slesvig, About the abandoned opportunities to hold plebiscites in 1848 and 1864 (Danish)
- Abstimmungsgebiet, Plebiscite Zones and how they were defined (German), Gesellschaft für Schleswig-Holsteinische Geschichte (Society for History of Schleswig-Holstein)
- Clausen-linien, The Clausen-Line and its background (Danish), Grænseforeningen
- Clausen, H.V., Før Afgørelsen [Before the Decision]), Gyldendalske Boghandel Nordisk Forlag, Copenhagen, 1918, p. 23 (Danish).
- Clausen, H.V., Før Afgørelsen [Before the Decision]), Gyldendalske Boghandel Nordisk Forlag, Copenhagen, 1918, p. 16 (Danish).
- Clausen, H.V., Før Afgørelsen [Before the Decision]), Gyldendalske Boghandel Nordisk Forlag, Copenhagen, 1918, pp. 24-25 (Danish).
- Tiedje.Linie, About the suggestion of Tiedje to modify the borderline (German)
- Mindretal 1920 - 1955, The minorities 1920 - 1955 (Danish), Institut for Historie, Kultur og Samfundsbeskrivelse / Universitet Syddanmark
- Tyskertid og genforening, The German Era and Reunification (Danish), German German Historical Museum
- Speech of Statsminister Niels Neergaard on the 11th of July 1920 after the transfer of Northern Schleswig to Denmark (Danish), Institut for Historie og Områdestudier / Aarhus Universitet