Austrian and Prussian troops cross the Eider into Denmark

Background. The conflict arose from the November Constitution of 1863, which tied the Duchy of Schleswig more closely to the Danish kingdom. This was viewed by the German side as a violation of the London Protocol. On 16 January 1864, Bismarck issued an ultimatum demanding the abolition of this constitution within 48 hours. Austria and Prussia declared they would act against Denmark without regard to the German Confederation's decisions.

The Crossing. Prussian and Austrian troops crossed into Schleswig on 1 February 1864. This action was taken against the resistance of the Federal Assembly of the German Confederation. The crossing marked the beginning of the war and the invasion of Jutland. The forces moved into the Danish fief, establishing the military phase of the conflict.

Political Context. The war began after the passing of the November Constitution, which established a shared law of succession and a common parliament for Schleswig and Denmark. King Christian IX signed this constitution on 18 November 1863. The German side considered this a violation of the London Protocol, leading to the ultimatum and subsequent military action.