The seat of war in Denmark, 1864. The Second Schleswig War was the second military conflict over the Schleswig-Holstein Question of the nineteenth century. The war began on 1 February 1864, when Prussian and Austrian forces crossed the border into the Danish fief Schleswig. Denmark fought troops of the Kingdom of Prussia and the Austrian Empire representing the German Confederation. The war ended on 30 October 1864, with the Treaty of Vienna and Denmarks cession of the Duchies of Schleswig (except for the island of ?r?, which remained Danish), Holstein and Saxe-Lauenburg to Prussia and Austria. From "Illustrated London News", 1864.