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Denmark had long held authority over the duchies of Schleswig and Holstein, territories at the intersection of Danish and German identities. For Denmark, Schleswig was central to its kingdom, while Holstein had a historical connection to the German Confederation although it had been under Danish influence. Tensions between the Danish Crown and the rising German nationalist movement had been building for decades, culminating in Denmark's 1863 decision to pass a constitution that aimed to formally integrate Schleswig into the Kingdom.