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."
Seven Years' War
Things were looking grim for Prussia now, with the Austrians mobilising to attack Prussian-controlled soil and a combined French and "Reichsarmee" (German states) army under Prince Soubise approaching from the west. The "Reichsarmee" was a collection of armies from the smaller German states that banded together to heed the appeal of the Holy Roman Emperor Franz I against Frederick. However, in November and December 1757, the whole situation in Germany was reversed. First, Frederick devastated Soubise's forces at the Battle of Rossbach on 5 November 1757 and then routed a vastly superior Austrian force at the Battle of Leuthen on 5 December 1757. Rossbach was the only battle between the French and the Prussians during the entire war. At Rossbach, the Prussians lost about 548 men killed while the Franco-German force under Soubise lost about 10,000 killed. Frederick always called Leuthen his greatest victory, an assessment shared by many at the time as the Austrian Army was considered to be a highly professional force. With these victories, Frederick once again established himself as Europe's premier general and his men as Europe's most accomplished soldiers. However, Frederick missed an opportunity to completely destroy the Austrian army at Leuthen; although depleted, it escaped back into Bohemia. He hoped the two smashing victories would bring Maria Theresa to the peace table, but she was determined not to negotiate until she had re-taken Silesia. Maria Theresa also improved the Austrians' command after Leuthen by replacing her incompetent brother-in-law, Charles of Lorraine, with von Daun, who was now a field marshal.