Frederick VII of Denmark
Three episodes proved fundamental to the unification of Germany. First, the death without male heirs of Frederick VII of Denmark led to the Second War of Schleswig in 1864. Second, the unification of Italy provided Prussia an ally against Austria in the Austro-Prussian War of 1866. Finally, France—fearing Hohenzollern encirclement—declared war on Prussia in 1870, resulting in the Franco-Prussian War. Through a combination of Bismarck's diplomacy and political leadership, von Roon's military reorganization, and von Moltke's military strategy, Prussia demonstrated that none of the European signatories of the 1815 peace treaty could guarantee Austria's sphere of influence in Central Europe, thus achieving Prussian hegemony in Germany and ending the dualism debate.