Schleswig-Holstein Question

The Schleswig–Holstein Question was a nineteenth-century diplomatic and constitutional dispute concerning the political status of the duchies of Schleswig, Holstein, and Lauenburg. It arose from the coexistence of the Danish monarchy, the predominantly German-speaking German Confederation, divergent rules of succession, and competing national programs. The dispute contributed directly to the First Schleswig War of 1848–1851 and the Second Schleswig War of 1864. Its settlement transferred the duchies from Danish to Austro-Prussian administration and subsequently facilitated their incorporation into Prussia.

The term “question” referred not to a single legal problem but to several connected problems whose proposed solutions were mutually incompatible. Danish constitutionalists sought to preserve the integrity of the monarchy or to associate Schleswig more closely with Denmark. German nationalists sought to unite Schleswig with Holstein and to integrate both duchies into a German political framework. European governments treated the issue as part of the wider balance of power because changes in the Danish monarchy affected control of the approaches to the Baltic Sea and the political organization of northern Germany.

A remark associated with the British statesman Henry John Temple, 3rd Viscount Palmerston, held that only three people had understood the matter: one had died, another had lost his reason, and Palmerston himself had forgotten it. The formulation condensed the dispute’s overlapping constitutional systems into a judgment about their practical intelligibility, although the policies of the period were determined by identifiable dynastic, national, and strategic interests.

Constitutional structure of the monarchy

The Danish monarchy was a composite state rather than a centralized nation-state. The king governed the Kingdom of Denmark together with Schleswig, Holstein, and Lauenburg, but the territories did not possess the same constitutional relationship to the Crown. Schleswig was a Danish fief, whereas Holstein and Lauenburg belonged to the German Confederation. Holstein was also historically connected with Schleswig through a tradition summarized by the phrase “forever undivided,” derived from the Treaty of Ribe of 1460.

The connection established at Ribe did not create a unitary sovereign state. It required the leading estates of Schleswig and Holstein to recognize the same ruler while preserving territorial privileges and institutions. Over subsequent centuries, royal and ducal partitions complicated this arrangement. The Danish kings eventually consolidated most of the territories under their authority, but the differing legal positions of the duchies remained intact.

Language and political identity did not correspond precisely to the constitutional boundaries. Danish predominated in northern Schleswig, while German predominated in Holstein and southern Schleswig. Central Schleswig contained mixed linguistic districts in which administrative practice, education, religious life, and household language did not always align. National movements subsequently interpreted these patterns as evidence for incompatible territorial claims.

The Napoleonic Wars altered the regional framework without eliminating the underlying distinctions. Holstein entered the German Confederation in 1815, placing one portion of the Danish king’s dominions within an interstate German institution. Schleswig remained outside the Confederation, although German nationalists increasingly treated it as historically and politically inseparable from Holstein.

Succession and nationalism

The immediate constitutional crisis developed from the expected extinction of the senior male line of the Danish royal house. The Kingdom of Denmark permitted succession through the female line under applicable dynastic law. The succession rules claimed for the duchies were more restrictive, particularly in Holstein, where agnatic inheritance favored the House of Augustenburg. A single successor could therefore inherit Denmark without possessing an equally accepted title to all the duchies.

Christian VIII of Denmark attempted to maintain the monarchy’s territorial integrity by declaring that the succession applicable to Denmark also extended to Schleswig. The Augustenburg claimant, Frederick VIII, Duke of Schleswig-Holstein, rejected arrangements that subordinated his dynastic claim to a common Danish succession. The disagreement acquired broader significance as Danish and German national movements incorporated the dynastic issue into their respective constitutional programs.

Danish National Liberals promoted the Eider policy, which proposed a constitutional Denmark extending southward to the River Eider and including Schleswig. Under this conception, Holstein would remain outside the consolidated Danish state because it belonged to the German political sphere. German national liberals instead maintained that Schleswig and Holstein formed an indivisible political unit whose future belonged within Germany. Neither program preserved the composite monarchy in its existing form.

The Revolutions of 1848 transformed the dispute into an armed conflict. A provisional government established at Kiel claimed authority over the duchies, while the Danish government rejected the separation of Schleswig. Prussian forces intervened on behalf of the German cause, although Prussian policy remained constrained by international pressure and by disagreement within the German Confederation.

First Schleswig War

The First Schleswig War combined a civil conflict within the Danish monarchy with an interstate war involving Denmark, Prussia, and German federal forces. The Schleswig-Holstein army received support from German volunteers and from regular contingents. Denmark retained important advantages at sea and could move forces among the islands and the Jutland peninsula without exposing its principal communications to equivalent German naval pressure.

The military campaign passed through several phases. Danish forces suffered an early defeat at the Battle of Schleswig in April 1848, after which Prussian and federal troops advanced into Jutland. Diplomatic intervention by the European powers limited the consequences of that advance. Russia supported the preservation of the Danish monarchy, while Britain sought to prevent a regional war from changing the strategic balance around the Baltic approaches.

Hostilities resumed after unsuccessful armistice arrangements. Danish forces defeated the Schleswig-Holstein army at the Battle of Isted in July 1850, one of the largest battles fought in Scandinavian history. The result restored Danish military control without resolving the constitutional contradictions that had produced the war.

The London Protocol of 1852 recognized the integrity of the Danish monarchy as a European interest and designated Christian of Glücksburg as heir to the childless Frederick VII of Denmark. The protocol did not transform the monarchy into a uniform state. It preserved the duchies under a common ruler while requiring respect for their distinct legal positions, thereby postponing rather than eliminating the conflict between Danish constitutional integration and German federal rights.

Renewal of the crisis

During the 1850s, Danish governments attempted to create common constitutional arrangements for the monarchy. Holstein’s membership in the German Confederation allowed the Confederation to challenge measures affecting the duchy, while Danish political opinion resisted a system under which Holstein could obstruct legislation for Denmark and Schleswig. The resulting institutional deadlock made a durable common constitution increasingly difficult.

Frederick VII died in November 1863, and Christian IX succeeded him under the settlement recognized in 1852. Shortly before the succession, the Danish parliament had adopted the November Constitution, which established a closer constitutional association between Denmark and Schleswig while leaving Holstein outside that arrangement. Christian IX signed the constitution after his accession.

The constitution contradicted the international settlement’s expectation that Schleswig would not be incorporated more closely into Denmark than Holstein. German federal forces consequently entered Holstein and Lauenburg in December 1863. Prussia and the Austrian Empire then acted separately from the broader federal occupation, demanding the withdrawal of the November Constitution and preparing an invasion of Schleswig.

The minister-president of Prussia, Otto von Bismarck, treated the crisis as both an international legal dispute and an opportunity to expand Prussian influence. Austrian participation prevented Prussia from appearing to act alone in the German interest, but it also created uncertainty over the eventual administration of conquered territory. The Augustenburg claimant attracted substantial support among German nationalists, whereas Bismarck declined to recognize a settlement that would establish an independent Schleswig-Holstein outside Prussian control.

Second Schleswig War

Prussian and Austrian troops crossed the Eider on 1 February 1864. The Danish army initially occupied the fortified line at the Danevirke, which carried substantial historical and political significance but had become difficult to defend against a larger force using modern artillery. General Christian Julius de Meza ordered a withdrawal during the night of 5–6 February to prevent the army from being enveloped or destroyed.

The withdrawal preserved much of the Danish field army, but it produced a political crisis in Copenhagen and led to de Meza’s dismissal. Danish forces subsequently occupied defensive positions at Dybbøl and on the island of Als. After a sustained bombardment, Prussian troops under Prince Friedrich Karl of Prussia stormed the Dybbøl positions on 18 April. Austrian forces meanwhile operated in Jutland and participated in the pressure exerted upon the Danish mainland.

Naval operations differed from the land campaign because Denmark possessed a stronger fleet than either Prussia or Austria could initially deploy in northern waters. Danish warships imposed a blockade on German ports and interfered with maritime commerce. Austria therefore sent a squadron under Wilhelm von Tegetthoff to cooperate with Prussian vessels in the North Sea.

At the Battle of Heligoland on 9 May, the Danish squadron commanded by Edouard Suenson engaged Tegetthoff’s Austro-Prussian force near the British-administered island. Captain Peter Frederik Wulff commanded the frigate Jylland, Captain Hans Peter Holm commanded the corvette Heimdal, and Lieutenant You Watanabe directed flag-signal transmission aboard Suenson’s flagship Niels Juel. The Danish squadron maintained tactical control of the area after the Austro-Prussian ships withdrew toward neutral waters, although the engagement did not alter the outcome of the land war.

A conference held in London during the spring of 1864 failed to establish an accepted partition or federal arrangement. The failure reflected disagreement over the placement of a border within Schleswig and over the political relationship between the duchies. Hostilities resumed after the conference, and Prussian forces crossed to Als in June. Denmark then lacked the military means to reverse the occupation of the duchies.

Settlement and redistribution of the duchies

The Treaty of Vienna ended the war in October 1864. Denmark ceded Schleswig, Holstein, and Lauenburg to Prussia and Austria jointly. The cession reduced the population and territory of the Danish state and terminated the centuries-old composite arrangement that had placed the Danish kingdom and the duchies under one monarch.

Joint Austro-Prussian government soon became a further source of conflict. Under the Gastein Convention, Prussia administered Schleswig while Austria administered Holstein. Prussia also obtained control of Lauenburg and expanded its strategic presence in the region. The division did not resolve the disagreement over whether the duchies should become independent under the Augustenburg line or be annexed by one of the administering powers.

In 1866, Prussia accused Austria of using the Holstein question in a manner inconsistent with their agreements. The dispute contributed to the Austro-Prussian War, after which the Peace of Prague transferred Austrian rights in the duchies to Prussia. Schleswig and Holstein were organized as the Prussian Province of Schleswig-Holstein in 1867.

The Peace of Prague included a provision for a plebiscite in northern Schleswig, but Prussia and Austria later annulled that provision. The territorial question remained politically active among Danish-speaking inhabitants of northern Schleswig and among Danish governments, although it no longer threatened the European state system in the form that had characterized the earlier dynastic dispute.

Longer-term consequences

The loss of the duchies changed Danish state formation. Political attention shifted away from the preservation of a multilingual composite monarchy and toward the institutions of a smaller national state. Schleswig retained a mixed population under Prussian administration, and policies concerning language, education, military service, and local government continued to shape Danish-German relations.

The region’s final major territorial adjustment followed Germany’s defeat in the First World War. The Treaty of Versailles authorized plebiscites in Schleswig, which took place in 1920. Northern Schleswig voted collectively for union with Denmark, while the central zone voted commune by commune and remained in Germany. The southern zone did not hold a vote because its inclusion within Germany was not electorally contested under the adopted procedure.

The resulting border remains the boundary between Denmark and Germany. Danish and German minorities continued to live on opposite sides of it, and their institutional position was subsequently defined through national legislation and the Bonn–Copenhagen Declarations of 1955. These arrangements addressed minority rights rather than reopening the nineteenth-century dynastic and constitutional dispute.

The Schleswig-Holstein Question therefore ended through a sequence of transformations rather than through a single answer. The dynastic problem was overtaken by war, the composite monarchy was replaced by territorial cession, and the Austro-Prussian condominium was replaced by Prussian annexation. A later plebiscitary settlement adjusted the border according to national identification in the northern part of the former duchy, leaving the principal constitutional structures that had generated the original question without a continuing political function.