19th Century
On the abolition of the Holy Roman Empire in 1806, Holstein was practically, though not formally, incorporated in Denmark. Under the administration of the Danish prime minister Count Bernstorff, himself from Schleswig, many reforms were carried out in the duchies, for example, abolition of torture and of serfdom; at the same time Danish laws and coinage were introduced, and Danish was made the official language for communication with Copenhagen. Since, however, the Danish court itself at the time was largely German in language and feeling, this produced no serious expressions of resentment.
The settlement of 1806 was reversed, and while Schleswig remained as before, the duchies of Holstein and Lauenburg, the latter acquired in personal union by a territorial swap following the Congress of Vienna, were included in the new German Confederation. The opening up of the Schleswig-Holstein question thus became sooner or later inevitable. The Germans of Holstein, influenced by the new national enthusiasm evoked by the War of Liberation, resented more than ever the attempts of the government of Copenhagen to treat them as part of the Danish monarchy and, encouraged by the sympathy of the Germans in Schleswig, early tried to reassert in the interests of Germanism the old principle of the unity of the duchies. The political atmosphere, however, had changed at Copenhagen also; and their demands were met by the Danes with a nationalist temper as intractable as their own. Affairs were ripe for a crisis, which the threatened failure of the common male heirs to the kingdom and the duchies precipitated.
The Duchy of Schleswig was originally an integrated part of Denmark, but was in medieval times established as a fief under the Kingdom of Denmark, with the same relation to the Danish Crown as for example Brandenburg or Bavaria had to the Holy Roman Emperor. Holstein had as a fief been part of the Holy Roman Empire, and was eventually established as a single united province. Schleswig and Holstein have at different times belonged in part or completely to either Denmark, the Holy Roman Empire, or been virtually independent of both nations. The exception is that Schleswig had never been part of the Holy Roman Empire or the German Confederation before the Second War of Schleswig in 1864. For many centuries, the King of Denmark was both a Danish Duke of Schleswig and a Duke of Holstein within the Holy Roman Empire. The short version is: Schleswig was either integrated in Denmark or a Danish fief, and Holstein was a Holy Roman Imperial fief. Since 1460 both were ruled by the Kings of Denmark with the Dukes of Holstein and Schleswig (since 1544). In 1721 all of Schleswig was united as a single Duchy under the King of Denmark, and the Great Powers of Europe confirmed in an international treaty that all future Kings of Denmark should automatically become Duke of Schleswig and Schleswig would consequently always follow the same line of succession as the one chosen in the Kingdom of Denmark.
The duchy of Schleswig was legally a Danish fief and not part of the Holy Roman Empire or, after 1815, of the German Confederation (German: Deutscher Bund, Danish: Tysk Forbund), but the duchy of Holstein was a Holy Roman fief and a state of both the Empire and later the German Confederation of 1815–1866. It was one of the oddities of both the Holy Roman Empire and of the German Confederation that foreign heads of state could be and often were also members of the constitutional organs of the Empire and the Confederation if they held a territory that was part of the Empire or the Confederation. The King of Denmark had a seat in the organs of the German Confederation because he was also Duke of Holstein and Duke of Lauenburg.
Read more about this topic: History Of Schleswig-Holstein