By the end of 1761, Prussia was losing the Seven Years’ War. Its coffers and manpower were spent. During the war, Prussia had lost 120 generals, 1500 officers, and over 100,000 men. All seemed lost.
Frederick himself said,
The Austrians are masters of Schweidnitz and the mountains, the Russians are behind the length of the Warthe from Kolberg to Posen…my every bale of hay, sack of money or batch of recruits only arriving by courtesy of the enemy or from his negligence. Austrians controlling the hills in Saxony, the Imperials the same in Thuringia, all our fortresses vulnerable in Silesia, in Pomerania, Stettin, Kustrin, even Berlin, at the mercy of the Russians.
In January 1762, though, a miracle occurred. Elizabeth, Tsarina of Russia, died. She had been one of Frederick’s most implacable foes, second only to Maria Theresa.
Not only that, but she was succeeded by her nephew, Peter III, a man of whom it may be fairly said that he worshipped Frederick. Peter detested the Russians and lionized Prussians, even going so far as to wear the uniform of a Prussian soldier, even as tsar. Peter III immediately made peace with Prussia and concluded an alliance with Frederick. With the abandonment of Russia, the other nations against Frederick no longer had the motivation nor the ability to conclusively finish the war, and by 1763, the Seven Years’ War was over, with Prussia having miraculously survived.