The Three Year War from 1848-50 fought over the Schleswig issue had ended with a Danish military victory over the Schleswig-Holstein insurgents but the political issue had not been solved. The Danish government wanted to annex the duchy of Schleswig to the Danish kingdom while the Prussian government under Bismarck, for internal political and strategic reasons, wanted Schleswig to finally became a part of Germany.

In this goal it was backed by Austria. In December 1863 Allied troops entered Holstein without interference from the Danish army and demanded that the Danish forces be withdrawn from Schleswig, The Danes rejected this ultimatum and on the 1st of February 1864 the war began.

The armies
The Danish Army consisted of three infantry divisions each with three brigades and a cavalry division. In all about 38.000 men who at the outbreak of the war were positioned along the Dannevirke, a line of ramparts stretching across parts of Schleswig. Besides being inferior in numbers the Danish Army was also inferior in weapons. While the Prussian soldiers were equipped with breech loaders the Danish soldiers still had muzzle loaders and which proved to be a serious shortcoming during the war. To make matters worse there was also a serious lack of officers. The Danish supreme commander was Lt. General de Meza.

The Prussian army consisted of 37 battalions, 29 squadrons and 110 guns, totalling 38.400 men. The Austrian army consisted of 20 battalions, 10 squadrons and 48 gun totalling 23.000 men. In all about 61.400 men. During the war the Prussian forces were reinforced by 64 gun and about 20.000 men. The supreme commander of the Prussian-Austrian army was Field Marshal von Wrangel.

Udover at være underlegen i antal mænd, var den danske hær også underlegen mvh. våben. Imens de preussiske soldater var udstyret med moderne bagladere, havde de danske soldater stadig forladere, og det viste sig at være en ulempe, selvom det ikke var så alvorlig som eftertiden gjorde det til. Hvad der var værre var, at hæren havde en alvorlig mangel på officerer i modsætning til den allierede hær. Øverstkommanderende for hæren var den aldrende, excentriske, men kompetente og populære General de Meza.

Den preussiske hær bestod af 37 battalioner, 29 eskadroner og 110 kanoner. I alt 38.400 mand. Den østrigske hær bestod af 20 battalioner, 10 eskadroner og 48 kanoner. I alt 23.000 mand. Samlet bestod den allierede hær altså af 61.400 mand. Under krigen blev den preussiske hær yderligere forstærket med 64 kanoner og 20.000 mænd. Øvertkommanderende for den preussisk-østrigske hær var Feltmarskal von Wrangel.

Krigen
Den 1. februar krydsede de allierede Ejder floden og fortsatte nordpå imod byen Mysunde, hvor det første alvorlige sammenstød foregik. Preusserne håbede på at krydse floden Slien og angribe Dannevirke fra flanken og i ryggen.

The war
On the 1st of February the Allied crossed the Ejder river and continued northwards toward Mysunde where the first serious action took place. The Prussian had hoped to cross the Slien River and attack the Dannevirke from the flank and the rear.

The attack on the town was repulsed, but despite this victory the situation for the Danish army remained serious. The Dannevirke was too long to defend with the number of troops available and a breakthrough could mean the destruction of the Danish army, Consequently de Meza decided to withdraw most of the army to the positions at Dybbol.

On the night of the 5th of February the Danish army retreated from the Dannevirke positions leaving behind most of their guns. It was several hours before the enemy became aware that the Danish positions had been abandoned, giving the Danes a head start.

It was a terrible retreat, a blizzard was blowing and the temperature was far below zero. Tired and freezing men were struggling to stay on their feet while the officers urged them to go forward.

At Sankelmark the pursuing Austrians caught up with the 7th Brigade under command of colonel Max Müller. After a bloody battle the Austrian attack was stopped and the retreat continued with the enemy slowly following. The next day the main part of the army arrived at Dybbol and Sonderborg. 10 men had frozen to death during the march and the remainder were completely exhausted. De Meza was dismissed after his decision to withdraw from Dannevirke, and replaced with General Gerlach.

The Battle of Dybboel
After some days the Battle by Dybboel began. The Danish outposts were forced back to the redoubts and then the heaviest bombardment in history began. For weeks thousand of grenades rained down on the Danish positions destroying the fortifications, dismounting guns and killing many soldiers. An attack on the 4th of April was beaten back, but the Prussians continued the bombardment and dug closer to the redoubts.

On the 18th of April the Prussian attacked the Danish positions again. The Danish defenders numbered 5000 in the redoubts and trenches and 6000 in reserve. The Prussians attack columns consisted of 11.000 in the first wave and 26.000 in reserve.

The outcome was never in doubt but the Danish positions only fell after a vicious hand to hand battle. A counterattack by the 8th Brigade broke down with heavy losses after it had advanced one km towards the Dybboel Mill, and it was forced back to the bridgehead, together with the few soldiers that had escaped from the redoubts.

As the last Danish defenders left the bridgehead, the bridges were destroyed and for the rest of the day an artillery duel took place. The Danes lost nearly 5000 men dead, wounded and prisoners. The German casualties were 1200 men.

The war in Jutland
While the main part of the army withdrew towards Dybbol with the Prussian army slowly following, the weak cavalry division and the 7th infantry regiment continued northward towards Kolding and Vejle. The Austrian army occupied Northern Slesvig but stopped at the border to Noerrejutland as they did not want to advance into Denmark itself.

However after pressure from Bismarck to occupy the whole of Jutland a Prussian and Austrian corps crossed the border on March 8th. The same day the Austrians took Vejle and the Danish forces retreated to Horsens and later to Vendsyssel. At Frederica, which had been successfully defended in 1849, the Prussians pushed the Danes back towards the town which once more had been made into a fortress. However, on the 26th the town was abandoned and the troop transferred to Fuenen.

The fall of Als
After the fall of the positions by Dybbol the main force of the Army was transferred to Fuenen where an attack was excepted, but it was decided that Als should be defended.

On the 9th of May, the same day as the Danish Navy defeated a combined Austrian-Prussian navy at the battle of Helgoland, a truce were negotiated and a peace conference was initiated in London with participants from most of the European countries. Unfortunately the negotiations broke down as the parties could not agree on a border and the war recommenced.

On the 26th of May the Prussian guns began to shell the Danish positions on Als. On the night of the 29th of June, 2500 Prussians soldiers began crossing the sound in small boats. The armoured ship Rolf Krake attempted to stop the crossing and for a while the enemy were in dire straits and the crossing was stopped, but due to a misunderstanding the ship suddenly turned around and steamed away and the Prussians continued the crossing. The Danish regiments were unable to stop the attack and after some days the last Danish soldiers were evacuated by ship from Als. Once again the Danish losses had been heavy. The battle for the island had cost the Danish Army nearly 3000 men in dead, wounded and captured.

The loss of Als was another chok or the Danish people and the government and it was decided to sue for peace. But the terms were very hard now. All of Schleswig, Holstein and Lauenborg were to be ceded to Germany. By this Denmark lost 40 % of her area and 20 % of her population.

The last battle
The last battle of the war took place at Lundby in the northern part of Jutland. It was a small insignificant battle but was nevertheless noticed around Europe. Here it was clearly shown how superior breech loader was when compared to the muzzle loader. One Danish company attacked a German company which had taken up position behind a stone wall. The Danes attacked over a distance of 600 m with fixed bayonets. In 3 rapidly fired salvoes the Danish soldiers were cut down. The attack broke down 30 m in front of the stone wall. By this time ¾ of the Danish company had been killed or wounded. The German losses were 3 wounded.

The war had ended as a disaster for Denmark. Any ideas of war as an political instrument had vanished and to the present day Danish foreign policy has been marked by this defeat.

After a plebiscite in 1920 the northern part of Schleswig was returned to Denmark.