Schleswig-Holstein, a historic region located on the southern Jutland Peninsula. It now comprises the German state of Schleswig-Holstein and the area of Denmark called Sonderjylland or North Slesvig. For centuries, the Danes and the Germans vied for possession of the region.

During the Middle Ages, the separate duchies of Schleswig (in the north) and Holstein (in the south) developed. In Holstein, the population was predominantly German; in Schleswig, German in the south and Danish in the north. In 1460 the duchies were united as a domain of the Danish king, although not as a part of Denmark.

In 1815 the Congress of Vienna made Holstein a state of the German Confederation, while also continuing the union of Schleswig and Holstein under the Danish crown. This relationship proved unworkable as nationalist feelings rose among the Danes and the Germans. There was a brief rebellion by Germans in the duchies in 1848. Then in 1864, following repeated Danish demands for annexation of Schleswig, war broke out between Denmark and the German states. As a result of the war, Prussia and Austria gained joint control of the duchies. Prussia took sole possession in 1866, when it defeated Austria in the Seven Weeks' War.

After World War I, a plebiscite was held. The people in northern Schleswig voted to join Denmark; the rest of Schleswig-Holstein remained German.