Why was the Eider River important in the Schleswig-Holstein question?

In the context of the Schleswig-Holstein question, the Eider River served as the traditional geographic and political frontier between the duchies of Schleswig and Holstein. Its importance stemmed from its role as a focal point for competing nationalist agendas during the 19th century.213

Danish nationalists, known as the "Eider-Danes," advocated for the Eider Program, which sought to establish the river as the formal national boundary of Denmark. By defining the Eider as the border, they aimed to incorporate Schleswig into the Danish state while detaching it from Holstein, which was a member of the German Confederation.243

Conversely, German nationalists sought to maintain the historical association between the two duchies, viewing them as a single entity that should be separated from Denmark and integrated into the German sphere. This fundamental disagreement over whether the Eider should act as a state border or merely a regional boundary fueled the political crises and military conflicts that culminated in the German-Danish War of 1864.2354