Why did Danish nationalists want Schleswig incorporated into Denmark?

Danish nationalists, particularly those within the National Liberal movement, sought to incorporate the duchy of Schleswig into Denmark based on the belief that it had historically belonged to the Danish kingdom for centuries.123

This political aspiration, known as the Eider Program, was driven by the following factors:

• National Boundary: Nationalists identified the Eider River—the traditional frontier between Schleswig and Holstein—as the natural and historical national boundary of Denmark.413
• Countering German Influence: The movement emerged as a direct response to German nationalist efforts to link Schleswig with Holstein and integrate both into the German Confederation.123
• Cultural and Linguistic Ties: While Schleswig was culturally and linguistically mixed, with a Danish-speaking majority in the north, nationalists aimed to secure the region against the growing influence of the German-speaking population in the south and the political pressure from German-aligned interests.413

By attempting to detach Schleswig from its historical association with Holstein, Danish nationalists hoped to solidify the integrity of the Danish realm.42