German and Austrian troops advance into Danish Schleswig, opening a six month war with the Danes
The Second Schleswig War between Denmark and the German Federation over the provinces of Schleswig and Holstein began with an advance of German and Austrian troops across the River Eider. The war lasted until July when the outmanned Danes were forced to sue for terms and saw the two provinces incorporated into northern Germany, thereby reducing Denmark by more than a third in both territory and population. (By John Osborne)
Michael Embree, Bismarck's First War: The Campaign of Schleswig and Jutland 1864 (Solihull, England: Helion and Company, Ltd, 2007), 43.