Schleswig is a borderland between the German and Danish-speaking world. (For the Danish Slesvig see here). Though prior to 1864 it was much closer to the Danish-speaking world, and afterward, it became much more German. Despite its older significance for Denmark, the region was also important for Germany, hosting the Kiel Canal and the cityscapes of German industrialization.
Schleswig was once an integral part of Denmark, it was originally colonized by Danes, who built a fortified border at the Eider River that held until 1864. The Nobility of Schleswig resisted integration into the Danish Crown, and German settlers from Holstein began to change the linguistic composition of the Duchy. By the 19th century, much of South Schleswig spoke a low-German dialect.
Denmark saw the region as part of Denmark, I made a separate page covering the destinations important for the Danish Crown.
For Germany, the significance of the region was largely symbolic. The victory in the War of 1864 had reunified a German population with the rest of the German-speaking world. The region would see the benefits of German industrialization, as evident in the period’s Historicist architecture and urban expansion. The Danish North would be oppressed and held significant resentment towards the German empire for the losses incurred during WWI. Inter-war plebiscites saw Denmark regain Northern Schleswig, settling the linguistic divide in a logical manner.
For the traveler in Schleswig, the key places to visit from the German perspective are Haderslev (Hadersleben in German), Flensburg, and Rendsburg. All three of which have substantial quantities of German historicist architecture and the latter two played a role in the German industrialization of the region.
