This map is part of a series of 24 animated maps showing the history of Europe and nations, 1815-1914.
The three duchies of Schleswig, Holstein and Lauenburg are in personal union with the Danish Crown. The population of the first is predominately Danish, while the other two are composed almost exclusively of Germans, and were included in the German Confederation at the time of the Congress of Vienna.
These duchies are a subject of contention between Denmark and Prussia: Danish opinion favors incorporating Schleswig into the kingdom, whereas German nationalists want to annex all three duchies.
In 1863, the King of Denmark promulgates a common constitution for Denmark and Schleswig. At the appeal of the duchy’s German population, Prussia and Austria intervene; defeated, the Danes are forced to cede Holstein to Austria, Schleswig and Lauenburg to Prussia.
In June 1866, Prussia invades Holstein, claiming poor administration of the duchy by Vienna. In the days that follow, Bismarck, disavowed by the Assembly, declares the Confederation dissolved, and enters into war against Austria.