Denmark rejects the Austrian-Prussian ultimatum over the Danish Constitution

Background. The November Constitution of 1863, signed by King Christian IX on 18 November, established a shared law of succession and a common parliament for Schleswig and Denmark. The German side viewed this as a violation of the London Protocol. The events of 1863 gave Prussia a pretext to engage in war with Denmark to seize Schleswig-Holstein, pleasing nationalists by "liberating" Germans from Danish rule. Domestically, Bismarck hoped to gain public support among Prussian liberals through such a "liberation".

Diplomatic Exchange. On 14 January 1864, Austria and Prussia declared they would act against Denmark independently of the German Confederation. On 16 January, Bismarck issued an ultimatum demanding the abolition of the November Constitution within 48 hours. The Danish government refused to comply, maintaining the constitutional link between Schleswig and Denmark. This rejection precipitated the military invasion.

Consequences. The rejection of the ultimatum made war inevitable. Prussian and Austrian troops crossed into Schleswig on 1 February 1864, acting against the resistance of the Federal Assembly of the German Confederation. The war had begun after the passing of the November Constitution, which the German side viewed as a violation of the London Protocol.