Why did Austria oppose Prussian plans to annex Schleswig-Holstein?

Austria’s opposition to Prussian plans to annex the duchies of Schleswig and Holstein was rooted in a broader struggle for hegemony within the German Confederation.12

Following the joint victory over Denmark in the German-Danish War of 1864, the two powers became co-sovereigns of the territories. Austria’s primary objective was to see the duchies established as an independent secondary state within the confederation, which would have bolstered its own influence and maintained a balance of power. Conversely, Prussia sought outright annexation or, at minimum, indirect control to expand its own power and secure strategic assets, such as a naval base at Kiel.123

This fundamental disagreement over the status of the duchies exacerbated the intense rivalry between the two nations, ultimately leading to the Seven Weeks’ War in 1866. Austria’s defeat in that conflict resulted in its exclusion from German affairs and allowed Prussia to annex the territories, fundamentally altering the European balance of power.12