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Second Schleswig War

War between Denmark, Prussia, and Austria in 1864

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The Second Schleswig War or German-Danish War, also sometimes known as the Dano-Prussian War or Prusso-Danish War, was the second military conflict over the Schleswig–Holstein question of the 19th century. The war began on 1 February 1864, when Prussian and Austrian forces crossed the border into the Danish fief Schleswig. Denmark fought troops of the Kingdom of Prussia and the Austrian Empire representing the German Confederation.

Like the First Schleswig War (1848–1852), it was fought for control of the duchies of Schleswig, Holstein, and Lauenburg. Succession disputes concerning the duchies arose when Frederick VII, King of Denmark died without an heir acceptable to the German Confederation. The war started after the passing of the November Constitution of 1863, which tied the Duchy of Schleswig more closely to the Danish kingdom, which was viewed by the German side as a violation of the London Protocol.

The war ended on 30 October 1864, with the Treaty of Vienna and Denmark's cession of the Duchies of Schleswig (except for the island of Ærø, which remained Danish), Holstein and Saxe-Lauenburg to Prussia and Austria.

Background

In 1848, Denmark received its first liberal constitution. At the same time, and partly as a consequence, the secessionist movement of the large German majority in Holstein and southern Schleswig was suppressed in the First Schleswig War (1848–51), when the Germans in both territories failed in their attempt to become a united, sovereign and independent state: at the time, King Frederik VII of Denmark was also duke of the duchies of Holstein and Schleswig. The movement continued throughout the 1850s and 1860s, however, as Denmark attempted to integrate the Duchy of Schleswig into the Danish kingdom, while liberal proponents of German unification expressed the wish to include the Danish-ruled duchies of Holstein and Schleswig in a Greater Germany. Holstein was completely ethnically German, had been a German fief before 1806 and was a part of the German Confederation from 1815. Schleswig was a Danish fief and was linguistically mixed between Low German, Danish and North Frisian.

Before the Middle Ages, the people of Schleswig spoke Danish and Frisian, and as late as the 18th century, many rural areas of southern Schleswig still spoke Danish. In the early 19th century, the northern and middle parts of Schleswig spoke Danish, but the language in the southern half had shifted to German. German culture was dominant among the clergy and nobility; Danish had a lower social status and was spoken mainly by the rural population. For centuries, while the rule of the king was absolute, these conditions had created few tensions. When liberal and egalitarian ideas spread and nationalist currents emerged about 1820, identification was mixed between Danish and German: the German elites in Schleswig wished to be a part of Germany, while the Danes wanted Schleswig to be more firmly integrated into Denmark proper. Furthermore, there was a grievance about tolls charged by Denmark on ships passing through the Danish Straits between the Baltic Sea and the North Sea. To avoid that expense, Prussia and Austria planned to construct the Kiel Canal, which could not be built as long as Denmark ruled Holstein.

Much of the dispute focused on the heir of King Frederik VII of Denmark. The Germans of Holstein and Schleswig supported the House of Augustenburg, a cadet branch of the Danish royal family, but the average Dane considered them too German and preferred the rival Glücksburg branch with Prince Christian of Glücksburg as the new sovereign. Prince Christian had served on the Danish side in the First Schleswig War (1848–1851). Both Britain and the Russian Empire wanted the Danish Straits, linking the North Sea to the Baltic Sea, to be controlled by a relatively weak power such as Denmark to allow their respective navies to either enter the Baltic, in the case of Britain, or exit the Baltic, in the case of Russia. During the First Schleswig war in 1848–49, Russia had threatened twice to enter the war on the side of Denmark, which proved to be the deciding factor in the outcome of the war.

The peace treaty that had ended the war in 1851 stipulated that the duchy of Schleswig should be treated the same as the duchy of Holstein regarding its relations with the Kingdom of Denmark. However, during the revisions of the 1848 constitution in the late 1850s and early 1860s, Holstein refused to acknowledge the revision, creating a crisis in which the parliament in Copenhagen ratified the revision but Holstein did not. In 1863, Frederik VII died, and the new Danish monarch, King Christian IX, ordered that the new constitution should apply to Schleswig and Denmark, but not to Holstein. This was a clear breach of the 1851 peace treaty and the London Protocol of 1852 and gave Prussia and the German Confederation a casus belli against Denmark. The German position was considerably more favourable than it had been thirteen years before, when Prussia had to give in due to the risk of military intervention by Britain, France and Russia on behalf of Denmark: France had colonial problems, not least with Britain. Otto von Bismarck had succeeded in obtaining cooperation from the Austrian Empire, which underlined its great power status within the German union, while Britain was upset that Denmark had violated the London Protocol.

To understand the Danish resolve in this question one must understand that the Danes regarded Schleswig as an ancient core region of Denmark. The southern part of Schleswig contains the ruins of the old Danish Viking "capital" Hedeby and the Danevirke fortification; its first sections were built around 400–500 CE, possibly to protect Denmark from migrating tribes during the age of migration. Before the Danes took possession of the area, around 500 CE, Schleswig was the home of the Angles, of which many migrated to Britain, where they later formed the Anglo-Saxon kingdoms; the remaining Angles are believed to have assimilated with the Danes, indeed the Angles and the Danes seem to have had a very close relationship as attested by the shared sagas of the early English and Danes. Thus, to suggest that the region did no longer fully belong to Denmark was seen as a great provocation to the Danes' ancestral claim to Schleswig.

The Germans, on the other hand, referred to medieval history: Already in 1326 and 1448, the Danish kings had accepted the almost complete independence of Schleswig from the Danish Crown. The Germans argued that the duchy had therefore not been part of Denmark proper for 400 years, but instead was "forever inseparable" (up ewich ungedeelt) from the German duchy of Holstein, something the Danish king had promised as early as 1460.

In short, the Danes considered Schleswig to be an integral part of Denmark and wished to make this clear by enacting a new constitution that excluded Holstein, while the Germans thought that Schleswig was inseparable from Holstein: If the Danish crown wished to treat the two Duchies differently, the only solution was, in their eyes, to get rid of Danish rule altogether. Both sides thus saw the other as the aggressor.

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