Why did Denmark revive the Eider Program in the early 1860s?

The revival of the Eider Program in the early 1860s was driven by a combination of rising Danish nationalism, the influence of Pan-Scandinavianism, and persistent interference by the German Confederation in the constitutional affairs of the duchies.12

Following the return of a moderate National Liberal government led by Carl Christian Hall in 1857, the Danish government sought to secure the integration of Schleswig into Denmark while effectively separating it from Holstein. By 1863, the Danish leadership believed the geopolitical climate was favorable for this move, specifically because they perceived Prussia to be preoccupied with a Polish rebellion against Russia. Additionally, the Danes held expectations of potential support from Sweden. These factors emboldened the government to pursue the "November constitution," which effectively annexed Schleswig to Denmark in direct violation of previous international agreements from 1851 and 1852.312