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The First Schleswig War (German: Schleswig-Holsteinischer Krieg) or Three Years' War (Danish: Treårskrigen) was the first round of military conflict in southern Denmark and northern Germany rooted in the Schleswig-Holstein Question, contesting the issue of who should control the Duchies of Schleswig and Holstein. The war, which lasted from 1848 to 1851, also involved troops from Prussia and Sweden. Ultimately, under international pressure, the Prussians had to withdraw their forces. As a result, the war ended in a Danish victory over the rebels and the signing of the London Protocol in 1852. A second conflict, the Second Schleswig War, erupted in 1864.
At the beginning of 1848, Denmark included the Duchy of Schleswig, and the king of Denmark ruled the duchies of Holstein and Saxe-Lauenburg within the German Confederation. The majority of the ethnic Germans in Denmark lived in these areas. Germans made up a third of the country's population, and the three duchies accounted for half of Denmark's economy. The Napoleonic Wars, which had ended in 1815, had fanned both Danish and German nationalism. Pan-German ideology had become highly influential in the decades prior to the wars, and writers such as Jacob Grimm (1785-1863) and the Norwegian Peter Andreas Munch (1810-1863) argued that the entire peninsula of Jutland had been populated by Germans before the arrival of the Danes and that therefore Germans could justifiably reclaim it. Jens Jacob Asmussen Worsaae (1821-1885), an archaeologist who had excavated parts of the Danevirke, countered the pro-German claims, writing pamphlets which argued that there was no way of knowing the language of the earliest inhabitants of Danish territory, that Germans had more solid historical claims to large parts of France and England, and that Slavs by the same reasoning could annex parts of eastern Germany.
The conflicting aims of Danish and German nationalists contributed to the outbreak of the First Schleswig War. Danish nationalists believed that Schleswig, but not Holstein, should be a part of Denmark, as Schleswig contained a large number of Danes, whilst Holstein did not. German nationalists believed that Schleswig, Holstein, and Lauenburg should remain united, and their belief that Schleswig and Holstein should not be separated led to the two duchies being referred to as Schleswig-Holstein. Schleswig became a particular source of contention, as it contained a large number of Danes, Germans and North Frisians. Another cause of the war was the legally questionable change to the rules of ducal succession in the duchies.
King Christian VIII of Denmark died in January 1848. His only legitimate son, the future Frederick VII, seemed unable to beget heirs, thus the duchies appeared likely to pass to the rule of the House of Oldenburg, which might have resulted in a division of Denmark. Accordingly, Christian VIII had decreed (8 July 1846) a change to the succession law in the duchies to allow succession through the female line. The implementation of this law was illegal.
The Schleswig-Holsteiners, being inspired from the successes of the French in the revolution in Paris of February 1848, sent a deputation to Copenhagen to demand the immediate recognition by King Frederick VII of a joint state of Schleswig-Holstein previous to its admittance into the German Confederation. King Frederick's reply, in which he admitted the right of Holstein as a German confederate state to be guided by the decrees of the Frankfurt diet, but declared that he had neither "the power, right, nor wish" to incorporate Schleswig into the confederation, was immediately followed or even perhaps preceded by an outbreak of open rebellion.
Schleswig-Holsteinian Prince Frederik of Noer took the 5th "Lauenburger" Rifle Corps (Jägerkorps) and some students of Kiel university to take over the fortress of Rendsburg in Schleswig-Holstein. The fortress contained the main armoury of the duchies, and the 14th, 15th, and 16th Infantry Battalions, the 2nd Regiment of Artillery, as well as some military engineers. When Noer's force arrived, they found that the gates to the fortress had been left open for an unknown reason and promptly walked in, surprising the would-be defenders. After delivering a speech to the defenders, the prince secured the allegiance of the battalions and regiment of artillery to the provisional government. Danish officers who had been serving in the defence of the fortress were allowed to leave for Denmark on the assurance that they did not fight against Schleswig-Holstein in the coming war.
Wishing to defeat Denmark before Prussian, Austrian, and German troops arrived to support them, 7,000 Schleswig-Holsteinish soldiers under General Krohn occupied Flensborg on 31 March. Over 7,000 Danish soldiers landed east of the city, and Krohn, fearing he would be surrounded, ordered his forces to withdraw. The Danes were able to reach the Schleswig-Holsteiners before they were able to retreat, and the subsequent Battle of Bov on 9 April was a Danish victory. At the battle, the Prince of Noer, senior commander of the Schleswig-Holsteinish forces, did not arrive until two hours after fighting had started, and the Schleswig-Holsteiners were more prepared for the withdrawal they had intended to make than for an engagement.
The Germans had embarked on this course of participation in the Schleswig-Holstein War alone, without the European powers. The other European powers were united in opposing any dismemberment of Denmark, even Austria refusing to assist in enforcing the German view. Swedish troops landed to assist the Danes; Tsar Nicholas I of Russia, speaking with authority as head of the senior Gottorp line, pointed out to King Frederick William IV of Prussia the risks of a collision. Great Britain, though the Danes had rejected her mediation, threatened to send her fleet to assist in preserving the status quo. The fact that Prussia had entered the war on behalf of the revolutionary forces in Schleswig-Holstein created a great number of ironies. The newly elected Frankfurt Diet tended to support the incursion into the Schleswig-Holstein War while King Frederick William did not. Indeed, Frederick William ordered Friedrich von Wrangel, commanding the army of the German Confederation, to withdraw his troops from the duchies; but the general refused, asserting that he was under the command of the Diet of the German Confederation[clarification needed] and not of the King of Prussia but of the regent of Germany (Archduke John of Austria). Wrangel proposed that, at the very least, any treaty concluded should be presented for ratification to the Frankfurt Diet. The Danes rejected this proposal and negotiations were broken off. Prussia was now confronted on the one side by the German nation urging her clamorously to action, on the other side by the European powers threatening dire consequences should she persist. After painful hesitation, Frederick William chose what seemed the lesser of two evils, and, on 26 August, Prussia signed a convention at Malmö which yielded to practically all the Danish demands. The Holstein estates appealed to the German diet, which hotly took up their cause, but it was soon clear that the central government had no means of enforcing its views. In the end the convention was ratified at Frankfurt. The convention was essentially nothing more than a truce establishing a temporary modus vivendi. The main issues, left unsettled, continued to be hotly debated.
In October, at a conference in London, Denmark suggested an arrangement on the basis of a separation of Schleswig from Holstein, which was about to become a member of a new German empire, with Schleswig having a separate constitution under the Danish crown.
In April 1850, Prussia, which had pulled out of the war after the treaty of Malmö,[clarification needed] proposed a definitive peace on the basis of the status quo ante bellum and postponement of all questions as to mutual rights. To Palmerston the basis seemed meaningless and the proposed settlement would settle nothing. Nicholas I, openly disgusted with Frederick William's submission to the Frankfurt Parliament, again intervened. To him Duke Christian of Augustenborg was a rebel. Russia had guaranteed Schleswig to the Danish crown by the 1773 Treaty of Tsarskoye Selo. As for Holstein, if the King of Denmark could not deal with the rebels there, he himself would intervene as he had done in Hungary. The threat was reinforced by the menace of the European situation. Austria and Prussia were on the verge of war, and the sole hope of preventing Russia from entering such a war on the side of Austria lay in settling the Schleswig-Holstein question in a manner desirable to her. The only alternative, an alliance with the hated Napoleon Bonaparte's nephew, Louis Napoleon, who was already dreaming of acquiring the Rhine frontier for France in return for his aid in establishing German sea-power by the ceding of the duchies, was abhorrent to Frederick William.
The Protocol affirmed the integrity of the Danish federation as a "European necessity and standing principle". Accordingly, the duchies of Schleswig (a Danish fief) and Holstein, and Lauenburg (sovereign states within the German Confederation) were joined by personal union with the King of Denmark. For this purpose, the line of succession to the duchies was modified, because Frederick VII of Denmark remained childless and hence a change in dynasty was in order. (The originally conflicting protocols of succession between the duchies and Denmark would have stipulated that, contrary to the treaty, the duchies of Holstein and Lauenburg would have had heads of state other than the King of Denmark.) Further, it was affirmed that the duchies were to remain as independent entities, and that Schleswig would have no greater constitutional affinity to Denmark than Holstein.
This settlement did not resolve the issue, as the German Diet had steadfastly refused to recognize the treaty, and asserted that the law of 1650 was still in force, by which the Duchies were not united to the state of Denmark, but only to the direct line of the Danish kings, and were to revert on its extinction, not to the branch of Glucksburg, but to the German ducal family of Augustenburg. Only twelve years passed before the Second Schleswig War in 1864 resulted in the incorporation of both duchies into the German Confederation, and later, in 1871, into the German Empire.
These three southern regions of the Danish "Gesamtstaat" or "Helstaten" (common name for the union of the kingdom and the duchies) made up about one half of the monarchy's economic power.
To prevent a division of the Danish kingdom, the Danish "Royal Law" (Lex Regia) was - illegaly [sic] - introduced in the duchies.