Austro-Prussian War
The pretext for the conflict was found in the dispute between Prussia and Austria over the administration of Schleswig-Holstein, which the two of them had conquered from Denmark and agreed to jointly occupy at the end of the Second Schleswig War in 1864. When Austria brought the dispute before the German Diet and also decided to convene the Diet of Holstein, Prussia declared that the Gastein Convention had thereby been nullified and invaded Holstein. When the German Diet responded by voting for a partial mobilization against Prussia, Bismarck claimed that the German Confederation was ended. Crown Prince Frederick "was the only member of the Prussian Crown Council to uphold the rights of the Duke of Augustenburg and oppose the idea of a war with Austria which he described as "fratricide"". Although he supported unification and the restoration of the medieval empire, "Fritz could not accept that war was the right way to unite Germany."
History of Austria
In 1745, following the reign of the Bavarian Elector as Emperor Charles VII, Maria Theresa's husband Francis of Lorraine, Grand Duke of Tuscany, was elected Emperor, restoring control of that position to the Habsburgs (or, rather, to the new composite house of Habsburg-Lorraine), Francis holding the titular crown until his death in 1765, but his empress consort Maria Theresa carrying out the executive functions. The Pragmatic Sanction of 1713 applied to the hereditary possessions of the Habsburgs and Archduchy of Austria but not the position of Holy Roman Emperor, which could not be held by women, thus Maria Theresa was Empress Consort not Empress Regnant.