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."
Military history of Germany
During the Seven Years' War, Prussia fought on the side of Britain against Russia, Sweden, Austria, France, and Saxony. Frederick II of Prussia first invaded Saxony and defeated a Saxon army at Lobositz. Frederick would then invade Bohemia, the Prussians besieged Prague, but they were defeated at Kolin. Since Prussia looked vulnerable, the Austrians and French invaded Prussian lands. However, the French were defeated at Rossbach and the Austrians at Leuthen. In 1758, Frederick the Great tried to invade Austria, but he failed. Now, the Russians tried to defeat the Prussians, but the Prussians earned a pyrrhic victory at the Zorndorf. The Swedes, however, fought the Prussians to a draw at Tornow. However, Austria gained a victory against the Prussian main army at Hochkirch. In 1759, the Prussians lost at Kunersdorf to the combined Russians and Austrians. Berlin itself was taken for a few days in 1762, but its army could not be destroyed. However, the great alliance against Prussia broke up when Elizabeth of Russia died. It was from her death that a pro-Prussian ruler, Peter III would sue for peace. It was thanks to this "miracle of the House of Brandenburg" and to the unshakable will of Frederick that Prussia survived.