This was a part of the all European Seven Years' War; Austria once more tried to get back Silesia (for the second time)while Federick attempted to grab Saxony. The collapse of the Anglo-Austrian Alliance in 1756 meant that Britain had now changed sides, and in this war they supported Prussia against their former allies the Austrians.
After battles in 1761–62 went well for Russian and Austrian forces, in January 1763 Austria was suddenly abandoned by his ally with the ascension of Peter III of Russia who recalled his army from within Berlin and Pomerania upon the death of Empress Elizabeth of Russia (d. 5 January 1762 [O.S. 25 December 1761]).
While Peter was assassinated himself the next summer, before Catherine the Great succeeded him and could once again bring Russia into an alliance, peace talks that were already in progress about the wider war had concluded in February 1763—and, worse for Austria, Peter had mediated an agreement between Prussia and Sweden, allowing Frederick II's forces to consolidate his position and bolster Prussia's claims in January and February. All these events were against Austria's interests. Consequently, Prussia was then confirmed with her Silesian possessions in the Treaty of Hubertusburg.