The Second Schleswig War (Danish: 2. Slesvigske Krig, German: Deutsch-Dänischer Krieg) was the second military conflict over the Schleswig-Holstein Question of the nineteenth century. The war began on 1 February 1864, when Prussian forces crossed the border into Schleswig.[a] Denmark fought the Kingdom of Prussia and the Austrian Empire. Like the First Schleswig War (1848–52), it was fought for control of the duchies of Holstein and Lauenburg, due to the succession disputes concerning them when the Danish king died without an heir acceptable to the German Confederation. Controversy arose due to the passing of the November Constitution, which integrated the Duchy of Schleswig into the Danish kingdom in violation of the London Protocol. Reasons for the war were the ethnic controversy in Schleswig and the co-existence of conflicting political systems within the Danish unitary state.
The secessionist movement of the large German majority in Holstein and southern Schleswig was suppressed in the First Schleswig War (1848–51), but the movement continued throughout the 1850s and 1860s, as Denmark attempted to integrate the Duchy of Schleswig into the Danish kingdom whilst proponents of German unification expressed the wish to include the Danish-ruled duchies of Holstein and Schleswig in a Greater Germany. Holstein was a part of the German Confederation and before 1806 a German fief and completely ethnically German, whereas Schleswig was a Danish fief and was linguistically mixed between German, Danish and North Frisian. The northern and middle parts of Schleswig spoke Danish but the language in the southern half had shifted gradually 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 egalitarian ideas spread and nationalist currents emerged about 1820, identification was mixed between Danish and German.
Furthermore, there was a grievance about tolls charged by Denmark on shipping passing through the Danish Straits between the Baltic Sea and the North Sea. To avoid that expense, Prussia planned to construct the Kiel Canal, which could not be built as Denmark ruled Holstein.
Much of the dispute focused on the heir of King Frederick 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). At the time, the king of Denmark was also duke of the duchies of Holstein and Schleswig. In 1848, Denmark had received its first free constitution and at the same time (and partly as a consequence) had fought a civil war with the Germans of Schleswig-Holstein, in which Prussia had intervened.
The peace treaty stipulated that the duchy of Schleswig should be treated the same as the duchy of Holstein in its relations with the Kingdom of Denmark. 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. That was a clear breach of the 1851 peace treaty and gave Prussia and the German union a casus belli against Denmark. The German situation was considerably more favorable than it had been fifteen 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 neutralized Russia politically and succeeded in obtaining cooperation from Austria which underlined its great power status within the German union.
The adoption of the Constitution of Denmark in 1849 complicated matters further, as many Danes wished for the new democratic constitution to apply to all Danes, including those in Schleswig. The constitutions of Holstein and Schleswig were dominated by the Estates system, giving more power to the most affluent members of society, with the result that both Schleswig and Holstein were politically dominated by a predominantly German class of landowners. Thus two systems of government co-existed within the same state: democracy in Denmark, and absolutism in Schleswig and Holstein.
The three units were governed by one cabinet, comprising liberal Danish ministers, who urged economic and social reforms, and conservative ministers of the Holstein nobility, who opposed political reform. This caused a deadlock for practical lawmaking. Moreover, Danish opponents of this so-called Unitary State (Helstaten) feared that Holstein's presence in the government and simultaneous membership of the German Confederation would lead to increased German interference with Schleswig, and even in purely Danish affairs.
In Copenhagen, the Palace and most of the administration supported a strict adherence to the status quo. The same applied to foreign powers, such as Great Britain, France and Russia, who would not accept a weakened Denmark in favour of Germany, nor a Prussia that had acquired Holstein with the important naval harbour of Kiel that controlled the entrance to the Baltic.
In 1858, the German Confederation deposed the 'union constitution' of the Danish monarchy concerning Holstein and Lauenburg, which were members of the Confederation. The two duchies were henceforth without any constitution, while the 'union constitution' still applied to Schleswig and Denmark proper.
As the heirless King Frederick VII grew older, Denmark's successive National-Liberal cabinets became increasingly focused on maintaining control of Schleswig following the king's demise.
The king died in 1863 at a particularly critical time; work on the November Constitution for the joint affairs of Denmark and Schleswig had just been completed, with the draft awaiting his signature.
The new King, Christian IX, felt compelled to sign the draft constitution on 18 November 1863, expressing grave concern, in the process.
This action caused outrage among the duchies' German population and a resolution was passed by the German Confederation at the initiative of the Prussian Prime Minister Otto von Bismarck, calling for the occupation of Holstein by Confederate forces. The Danish government abandoned Holstein and pulled the Danish Army back to the border between Schleswig and Holstein. Most of it fortified itself behind the Danevirke. This order to retreat without combat caused adverse comment among some Danish private soldiers, but the military circumstances made it wise to shorten the frontier needed to be defended. Also, as the administrations of Holstein and Lauenburg were members of the German Confederation, not pulling back might have caused a severe political crisis and perhaps war.
There were so-called "flank positions" near Ebeltoft (North), the fortified city of Fredericia (center), and Dybbøl in the south designed to support the strategy of defending the peninsula of Jutland along the north-south axis using naval supremacy to move the army north-south and hence trap an invading army in futile marches between these flank positions. This would deny the (assumed superior) invader the chance of forcing the defenders into a decisive battle, and give the defenders the opportunity to swiftly mass and counter-attack weak enemy positions, besieging forces, or divided forces by shifting weight by sea transport. The political dimension of this strategy was to draw out the war and hence give time and opportunity for the "great powers" to intervene diplomatically—it was assumed that such an intervention would be to the advantage of (neutral) Denmark. This strategy had been successful in the First Schleswig War.
Unrealistic expectations of the potency of the Danish army and incompetence at the political level had overruled the command of the army's wishes to defend Jutland according to the above plan, and instead favoured a frontal defense of Jutland on or near the historical defense (and legendary border) line at the Danevirke, near the city of Schleswig in the south. Hence resources had been put into the Danevirke line and not into the flank positions, which stayed akin to battlefield fortifications rather than modern fortifications capable of withstanding a modern bombardment.
The problem with the Danevirke line was that perhaps it was relatively strong against a frontal assault but leaned on bodies of water or marshes at both ends. In early 1864, these waters and marshes froze solid in a hard winter letting the Germans bypass the Danevirke. The first attempt to bypass the position failed near Missunde, but eventually the Germans appeared in force in the Danevirke's rear, compelling the Danish high command to order the line abandoned. As this decision was taken in violation of direct orders from the Danish government and in opposition to public opinion in Denmark, General de Meza was relieved of his command and replaced by the more loyal General Gerlach.
The Danish army then occupied another fortified line called "the old Dybbøl". This position did not bar the entrance to Jutland but only the tip of a peninsula jutting into the Baltic Sea. There is little doubt that the command of the army did not believe that they could successfully repulse a well-prepared German siege and consequent assault on the Dybbøl position, and assumed that the political level would let the army be evacuated by sea and then fight the war on the principles of the north-south axis strategy.
But the political level did not appreciate the gravity of the situation, insisting on maintaining military presence in Schleswig and at the same time refused more modest German demands of peace. Hence the army was ordered to defend the Dybbøl position "to the last man", and consequently the siege of Dybbøl began.
The only railways in 1864 in Denmark north of the Kongeå were a line in Sjælland from Copenhagen to Korsør, and one in northern Jutland from Århus to the northwest. Any reinforcements for the Danevirke from Copenhagen would have gone by rail to Korsør and thence by ship to Flensburg, taking two or three days, if not hindered by storm or sea-ice. There was a good railway system in the duchies, but not further north than Flensburg and Husum.
Schleswig city, Flensburg, Sønderborg, and Dybbøl were all connected by a road paved with crushed rock, this being the route the army took. The same road continued from Flensburg to Fredericia and Århus and this was the route later taken by the Prussian army when it invaded Jutland.
On 18 November 1863, King Christian IX of Denmark signed the so-called "November constitution" establishing a shared law of succession and a common parliament for both Schleswig and Denmark. This was seen by the German Confederation as a violation of the 1852 London Protocol. In response, on 24 December 1863, Saxon and Hanoverian troops marched into Holstein on behalf of the Confederation (as part as the federal execution (Bundesexekution) against Holstein). Supported by the German soldiers and by loyal Holsteiners, Frederick VIII, Duke of Schleswig-Holstein took control of the government of Holstein.
In January the situation remained tense but without fighting; Danish forces controlled the north bank of the Eider River and German forces the south bank. On 14 January 1864, Austria and Prussia declared furthermore to take action against Denmark without regard to decisions of the German Confederation. On 16 January 1864, Bismarck issued an ultimatum to Denmark demanding that the November Constitution should be abolished within 48 hours. This was politically impossible, particularly given the short deadline, and the demand was consequently rejected by the Danish government.
All the inland waters (Eider River, Treene, Schlei, and the marshes east of Husum and around the Rheider Au) that the Danes were relying on as defence to guard the flanks of the Dannevirke, were frozen hard and could be crossed easily.
At the start of the war, the Danish army consisted of about 38,000 men in four divisions. The 8th Brigade consisted of the 9th and 20th Regiments (approximately 1,600 soldiers each), mainly soldiers from the middle and west and north of Jutland. About 36,000 men defended the Dannevirke, a job which it was said would have needed 50,000 men to do properly. The 1st Regiment had been changed from a battalion to a regiment on 1 December 1863. 
The Prussian army had 37 battalions, 29 squadrons and 110 guns, approximately 38,400 men. The Austrian army had 20 battalions, 10 squadrons and 48 guns, approximately 23,000 men. During the war the Prussian army was strengthened with 64 guns and 20,000 men. The supreme commander for the Prussian-Austrian army was Field Marshal Friedrich Graf von Wrangel.
Prussian and Austrian troops crossed into Schleswig on 1 February 1864 against the resistance of the Federal Assembly of the German Confederation, and war became inevitable. The Austrians attacked towards the refortified Dannevirke frontally while the Prussian forces struck the Danish fortifications at Mysunde (on the Schlei coast of Schwansen east of Schleswig town), trying to bypass the Danevirke by crossing the frozen Schlei inlet, but in six hours could not take the Danish positions, and retreated.
In the Battle for Königshügel (Danish Kongshøj, translated King's Hill) near Selk on 3 February 1864, Austrian forces commanded by General Gondrecourt pushed the Danes back to the Dannevirke. The Danish 6th Brigade had an important part. The battle was fought in a snowstorm at −10 °C (14 °F). Danish fighting against Austrians at Selk and Kongshøj and Saksarmen on February 3, 1864 is described as follows:
The enemy sharpshooters immediately got reinforcement of a whole battalion, which advanced in a column with a music band which blew a storm-march, the battalion's commander followed on a horse, and after that the battalion's standard. Captain Stockfleth ordered his men to fire on the band and the battalion's commander and the standard-bearer. After that the storm-march sounded not so beautiful now that that lacked quite a few voices. The battalion commander's horse was shot under him. He grasped the standard when the standard-bearer fell, and now it went forward again with great strength.— , This link
A Danish military report dated 11 February 1864 describes incidents near Königshügel/Kongshøj and Vedelspang as follows:
On the 3 February the Regiment's 1st Battalion occupied the Brigade's forward post line while its 2 Battalion stood as a reserve in Bustrup. The company commanders Daue and Steinmann under Major Schack's command increased its main position near Vedelspang while the Stockfleth Company stood between Niederselk and Alten Mühle as well as the Riise Company behind the dam near Haddeby. The, 9. Regiment found its place about 1.30 p.m. and attacked an enemy unit which was coming from Geltorf and Brekendorf. The Stockfleth Company's main position, coming from Vedelspang, had advanced to Kongshøi, and Kastede the same distance behind the Danevirke rampart in front of Bustrup. In Bustrup the shooting was heard about 2 p.m. 2nd Battalion occupied the rampart and covered the withdrawing squads. The enemy pressed intensely in the east towards Haddebyer Noor, but was stopped here and remained fighting in one place until it turned dark. They sent a company to drive away the enemy from Vedelspang, but could not press further on than to towards the north part of the exercise ground.
The regiment's losses in this fighting: Dead, 1 corporal 1 undercorporal 7 privates; wounded, 2 corporals 3 undercorporals 18 privates; missing 11 privates.— Fredericia 11 February 1864, Scholten, Oberstlieutenant and Regimentscommandeur., report
On 5 February 1864, the Danish commander-in-chief, lieutenant general Christian Julius De Meza, abandoned the Dannevirke by night to avoid being surrounded and withdrew his army to Flensburg; 600 men were captured or killed, ten of them frozen to death; he was also forced to abandon important heavy artillery.
The railway from the south to Flensburg was never properly used during this evacuation and the Danish army only evacuated what men and horses could carry or pull by road, leaving behind much artillery, most importantly heavy artillery. Some hours later, the Prussians and Austrians discovered the retreat and started to pursue.
This withdrawal to Als and Dybbøl has gone down in Danish history as one of the worst that Danish soldiers have been exposed to. Some of them compared it to Napoleon's retreat from Moscow. It was northwards in a north gale with driven snow, and most of the soldiers had had no rest for the last four days and nights:image. The march was burdened with artillery guns and supply carts and had to be as slow as its slowest component. Men and horses had trouble standing. Horses could not carry or pull their loads properly because of the snow and ice; riders had to dismount and lead their horses. Artillery guns and carts overturned. The column of men and horses and vehicles seemed endless. The army had to march from the Danevirke to Flensburg, which took about 14–18 hours. (Schleswig (town) by the east end of the Danevirke is 20 miles from Flensburg as the crow flies, but further by road, plus getting from their positions to Schleswig town first.) They also had to fight rearguard against pursuing Prussians and Austrians. Some men in sight of Flensburg and thankful for the coming rest were ordered to stop or go back to man checkpoints. Many men were missing at the roll call, and it was thought that the many Schleswig men among the soldiers would desert the march on the way and go home; but most of them came in that morning or the next morning.
Near Stolk-Helligbek, about 10 kilometers north of Schleswig, pursuing Austrians reached them, and in heavy fighting near Oversø, the 9th and 20th Regiments of the 8th Brigade lost 600 men dead, injured and captured. On that day ten Danish soldiers died of hypothermia.
In the Battle of Sankelmark (about eight kilometers south of Flensburg) pursuing Austrians caught up with the Danish rear party, which consisted of the 1st and 11th regiments. The Danes were commanded by Colonel Max Müller. A hard fight, where large parts of 1st Regiment were taken prisoner, stopped the Austrians, and the retreat could continue. However, the Danes lost more than 500 men there. After a short rest and some food and drink in Flensburg, the 8th Brigade had to march to Sønderborg, where they were taken by ship to Fredericia; the ship was so loaded that the men could not lie down, and on deck they had no shelter from the winter weather. Other units stayed in Dybbøl; a report says that some were so exhausted on arrival that they lay on the ground in heaps three or four deep to sleep.
The loss of the Dannevirke without a fight, which in the 19th century played a big role in Danish national mythology due to its long history, caused a substantial psychological shock in Denmark and, as a result, de Meza had to resign from supreme command. Denmark never again ruled the Dannevirke. The Austrians, under Ludwig Karl Wilhelm von Gablenz, marched north from Flensburg, while the Prussians advanced east on Sønderborg.
On 18 February 1864, some Prussian hussars, in the excitement of a cavalry skirmish, crossed the north frontier of Schleswig into Denmark proper and occupied the town of Kolding. An invasion of Denmark itself had not been part of the original programme of the allies. Bismarck determined to use this circumstance to revise the whole situation. He urged upon Austria the necessity for a strong policy, to settle, comprehensively, the question of the duchies and the wider question of the German Confederation; Austria reluctantly consented to press the war.
The Austrian army decided to stop at the north frontier of Schleswig. Some Prussians moved against Kolding and Vejle. On 22 February 1864, Prussian troops attacked the Danish forward line at Dybbøl, pushing them back to the main defence line.
The preliminaries of a peace treaty were signed on 1 August 1864: the King of Denmark renounced all his rights in the duchies in favour of the Emperor of Austria and the King of Prussia.
In the Treaty of Vienna, 30 October 1864, Denmark ceded Schleswig, Holstein and Lauenburg to Prussia and Austria. Denmark was also forced to surrender the enclaves in western Schleswig that were legally part of Denmark proper and not part of Schleswig, but was allowed to keep the island of Ærø (which had been administered as part of Schleswig), the town of Ribe and its surrounding land, and eight parishes from Tyrstrup Herred south of Kolding. As a result of the peace settlement, the land area of the Danish monarchy decreased by 40% and the total population reduced from 2.6 million to 1.6 million (about 38.5%). The Danish frontier had retreated about 250 km as measured from the furthest corner of the Duchy of Lauenburg to the new frontier on the Kongeå river.
In the Prussian forces' first clash of arms since reorganization, their effectiveness proved clear, something the Austrians ignored to their cost 18 months later in the Austro-Prussian War, and contributed to a perception in the German states that Prussia was the only state that could defend the other German states against external aggression. (See Unification of Germany.) Prussia and Austria took over the respective administration of Schleswig and Holstein under the Gastein Convention of 14 August 1865. About 200,000 Danes came under German rule.
Following the loss, Christian IX went behind the backs of the Danish government to contact the Prussians, offering that the whole of Denmark could join the German confederation, if Denmark could stay united with Schleswig and Holstein. This proposal was rejected by Bismarck, who feared that the ethnic strife in Schleswig between Danes and Germans would then stay unresolved. Christian IX's negotiations were not publicly known until published in the 2010 book Dommedag Als by Tom Buk-Swienty, who had been given access to the royal archives by Queen Margrethe II.
The Peace of Prague in 1866 confirmed Denmark's cession of the two duchies, but promised a plebiscite to decide whether north Schleswig wished to return to Danish rule. This provision was unilaterally set aside by a resolution of Prussia and Austria in 1878.
The war also shocked Denmark out of any idea of using war as a political tool. Danish forces were not involved in war outside their frontiers until the 1999 NATO bombing of the Federal Republic of Yugoslavia. It became clear that, against the might of Germany, Denmark could not assert her survival with her own arms; this played a crucial role in the "adjustment policy" and later "Cooperation policy" during the Nazi-German occupation in World War II.
From a Danish perspective, perhaps the most grievous consequence of the defeat was that thousands of Danes living in the ceded lands were conscripted into the German army in World War I and suffered huge casualties on the Western Front. This is still (but waning in time as the children of the conscripted men are dying out) a cause of resentment among many families in the southern parts of Jutland and the direct reason why a German offer of a joint centenary anniversary in 1966 was rejected.
After Germany's defeat in 1918, the Danish government asked the Allied Powers and the Versailles Conference of 1919 to include a plebiscite in the disputed 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. As a result of the plebiscite, North Schleswig was returned to Denmark.
Danish author Herman Bang wrote about the war and its effects on the island of Als in his novel Tine, published in 1889. The book has been translated into many languages, including English, and is considered to be an example of an impressionist novel.
In his novel The Riddle of the Sands (1903), Irish novelist Erskine Childers refers to the Dybbøl, when protagonists Davies and Carruthers encounter the (then present) German victory monument during a stop at Sønderborg on their Baltic yachting expedition.
In the M. R. James short story Nr. 13 references are made to the war. "Is this," he said, "the Danish courage I have heard so much of? It isn't a German in there; and if it was, we are five to one."
The 2014 Danish TV series 1864 depicts the Second Schleswig War.
The protagonist of the movie The Salvation is a veteran of the Second Schleswig War, who emigrates to America.