The Danish TV series 1864 is set in the year of the Second Schleswig War, fought between Denmark on one side, and Austria and Prussia on the other. It was sparked by the belief on the German side that Denmark was violating the principles of the London Protocol. Denmark attempted to write a new constitution which annexed the Duchies of Schleswig and Holstein, while the Germanic nations were unhappy with succession plans following the death of King Frederick VII in 1863; he had died with no legitimate heir making it hard to find a new ruler acceptable across all the duchies of Denmark.
The King had also been Duke of Schleswig and Holstein, but notably this was as well as being King of Denmark - the two duchies were not considered part of the country. Until, that is, the new constitution attempted to move them inside the Danish borders.
The January 30th 1864 edition of The York Herald had a go at explaining the complicated situation to its readers:
The sudden death of Frederick VII prevented the constitution [incorporating Schleswig and Holstein into Denmark] from being carried out, although it had received the sanction of the Rigsraad [the Danish National Parliament] and one of the first acts which [new King of Denmark] Christian IX performed on his ascending the throne was to accept and promulgate the new constitution.
But in so doing his majesty incurred the displeasure of the Germans, who contend that the Danes have no power to alter the system of government which has so long existed in the two Duchies, while many of them, especially the Governments of the smaller States, go so far as the deny the right of Christian IX to the rulership of these provinces, although the succession was determined in his favour of the Treaty of London in 1852, the signatories to which included the two very powers that are now threatening the invasion of Schleswig.
With regard to Holstein, it seems to be admitted that the Danes were in the wrong when they sought to incorporate that Duchy with the nation by making one common constitution for the whole.
There is no doubt that the King of Denmark, as Duke of Holstein, is a member of the Federal Diet, and that while he is the ruler, at the same time Holstein belongs to the Germanic Confederation. The Diet therefore have said, in effect, "The Duke Of Holstein has no power to make a new constitution for the Duchy, and if he insists on violating the general compact, we will teach him a lesson."
By the advice of the English Government, tendered through Lord Wodehouse, the King suspended the Holstein constitution and also withdrew the Danish troops from the Duchy, in order to avoid a collision with the Federal [German] soldiers.
But this concession seems, in the eyes of the Germans, to be only a reason for demanding others, and the Austrian and Prussian Governments now require the withdrawal of the Schleswig constitution. [...] But the King of Denmark has no legal authority to suspend the Schleswig Constitution, inasmuch as it has received the approval of the Rigsraad, and it is the Rigsraad which alone can repeal its own acts. The Austrian-Prussian summons, however, required the concession being made in a couple of days. But as the Danish Parliament was not siting, this demand could not be complied with. [...] The advance of the Austro-Prussian vanguard towards the Eider is an ominous sign, and makes us tremble for the future.
Well the editors of the Herald might tremble - the Eider was one of Denamrk's defence lines, but in January the river was frozen solid, and easy to cross.
The Aberdeen Journal of February 3rd told its readers that on Monday, the first of the month, the peace had shattered:
The Monday afternoon telegram brought word that shots had been exchanged on the Eider, that the Danes had blown up the bridges at Rendsburg to prevent the passage of the invading army and that the troops were eager for war and waiting in enthusiastic loyalty for the appearance of the King. [He] was on his way to the army, which he promised to join immediately that the war should break out.
Yesterday's [Tuesday] news shews this to have been too true. The only collision has been a skirmish of outposts. But war has begun and the hope now is, as the Danes have returned from the Kronewerk to the Dannewerk, and as the Rigsraad has been convoked by the King's ordiance, that they may evacuate Schleswig.
The funds [the financial markets] do not show much confidence in the prospect of peace, and the belief is that Denamrk will not long stand single-handed, and that the Germans are entering madly on a crisis in European history which will settle and unsettle questions which the French Emperor's Congress would never have dared to touch.
The war didn't extend beyond the initial combatants, and by July 1864 the Danes had suffered a series of setbacks which saw the entire mainland of the country occupied by Austrian and Prussian troops. The country sued for peace rather than risk the islands, and with them Copenhagen, falling. A ceasefire was signed on August 1st; a formal Treaty, the Treaty of Vienna, was signed on October 30th.
The two victors would be at war with each other in less than two years - the Austro-Prussian war - while the effectiveness of the Prussian military machine influenced smaller states towards favouring Prussia as a leader in the unification of Germany. Prussia, it was felt, could offer protection if the states bound themselves together.
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