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."
Diplomatic Revolution
Maria Theresa's diplomats, after securing French neutrality, actively began to establish an anti-Prussian coalition. Austria's actions alerted Frederick II, who decided to strike first by invading Saxony, commencing the Seven Years' War (1756–1763). Frederick's actions were meant to scare Russia out of supporting Austria (the two countries had previously entered into a defensive alliance in 1746). However, by invading Saxony, Frederick had inflamed his enemies; Russia, under the direction of Empress Elizabeth, sent an additional 80,000 troops to Austria. One year after the signing of the First Treaty of Versailles, France and Austria signed a new offensive alliance, the Second Treaty of Versailles, on 1 May 1757.