The introduction of a constitution for the ›composite state‹ by the Danish king, which also covered the duchies of Schleswig and Holstein, resulted in uprisings there in 1848. A considerable part of the population of the duchies wanted independence and was supported by forces sent from the German Confederation. They were, however, defeated by the Danes at the Battle of Idstedt.

In 1863, King Christian IX passed a new Danish Basic Law, which envisaged the incorporation of Schleswig into the kingdom: this was an affront of constitutional proportions, which was cleverly exploited by Bismarck for his objective of a unified German empire. Help promised to Denmark by Norway and Sweden never arrived. In the name of the German Confederation, Austria and Prussia attacked Denmark in 1864 and occupied the duchies. This was instrumental in the relegation of Denmark, once a European power, to the status of a small nation.