The Seven Years’ War, on which he embarked thus soon became a life-and-death struggle. In 1757 France, Sweden, Russia, and many of the smaller German states joined the ranks of his opponents, while the Prussian invasion of Bohemia collapsed after a serious defeat at Kolín in June. Brilliant victories over the French and Austrian armies, respectively, at Rossbach and Leuthen in November and December partially reestablished Frederick’s position, but it still remained extremely precarious. Ruthless exploitation of every available resource (notably of much of Saxony, which was under Prussian military occupation during most of the war), debasement of the currency, and a British subsidy that he received in 1758–62 allowed Frederick with increasing difficulty to keep up the unequal struggle. More than anything, however, he was helped by the complete failure of his enemies to cooperate effectively, while a partly British and British-financed army in western Germany from 1758 onward neutralized the French military effort. Nevertheless, the strain was immense; in October 1757 a cabinet order suspended all payment of salaries and pensions to Prussian civil servants and judges apart from diplomats serving abroad. Frederick could still win victories in the field, as, for example, at Zorndorf (August 1758) against the Russians at heavy cost or at Liegnitz and Torgau (August and November 1760) against the Austrians. But he also suffered serious defeats at Hochkirch in October 1758 and above all at the hands of a Russian army at Kunersdorf in August 1759. This disaster temporarily reduced him to despair and thoughts of suicide; if it had been effectively followed up by his adversaries, he could not have continued the struggle. As the forces he could put in the field dwindled and resistance grew among his subjects to the unprecedented burdens imposed by the war (in 1760 the landowners of Brandenburg refused to contribute further), the Prussian position became increasingly difficult; by 1761 it was desperate. However, the death in January 1762 of the empress Elizabeth, the most bitter of all Frederick’s enemies, completely changed the situation. Her successor, Peter III, a fanatical admirer of Prussia and Frederick, signed an armistice in May, followed by a Russo-Prussian peace treaty. This turn of events ended Maria Theresa’s hopes of recovering Silesia. The Treaty of Hubertusburg (Feb. 15, 1763), which ended the war in Germany, left the province in Frederick’s hands. Prussia had survived, and its military reputation was now greater than ever. The cost had been enormous, however. The Prussian army had lost 180,000 men during the struggle, and some Prussian provinces had been completely devastated.

Henceforth Frederick was determined to avoid another such conflict: the alliance with Russia that he signed in 1764 and which lasted until 1780 was directed largely to this end. Nevertheless, he still firmly opposed any growth of Habsburg power in Germany, and in July 1778 a new Austro-Prussian struggle broke out over the efforts of the emperor Joseph II, the son of Maria Theresa, to gain a large part of Bavaria. This War of the Bavarian Succession was half-hearted and short-lived, and the Treaty of Teschen ending it in May 1779 was a severe check to Joseph’s ambitions and a diplomatic victory for Frederick. But this new conflict showed unmistakably that Austro-Prussian rivalry stemming from the events of 1740–41 was now a deeply ingrained fact of German political life. Fear of Habsburg ambitions continued to haunt Frederick to the end of his reign. His last significant achievement was to inspire the formation, in July 1785, of the League of Princes (Fürstenbund), which united a number of German states—the most important being Hanover, Saxony, and the archbishopric of Mainz—in successful opposition to Joseph II and his renewed efforts to acquire the whole of Bavaria in exchange for the Austrian Netherlands.

Partition of Poland

The most important foreign policy development in the second half of Frederick’s reign was the first partition of Poland, in 1772. By this Prussia gained the Polish province of West Prussia (though without the great commercial city of Danzig), and thus Brandenburg and Pomerania, the core of the monarchy, became linked with the theretofore isolated East Prussia. This gave the state a much greater territorial coherence and more defensible frontiers. It also moved its geographic centre decisively to the east and sharpened the social and political differences that tended to separate it from the states of western Europe.

Frederick had always hoped for territorial gains of this kind, and, as the weakness and confusion of the internally divided Polish republic increased during the 1760s, the possibilities of realizing them grew. In 1769 he tried indirectly to interest Catherine II of Russia in a partition but in vain. By January 1771, however, faced by strong Austrian opposition to her expansionist ambitions in southeastern Europe, the empress had changed her mind. The visit to St. Petersburg in that month of Frederick’s younger brother Prince Henry played a decisive role in making a partition possible; the Habsburg government, which had hoped to recover Silesia or gain territory in the Balkans, was persuaded to join in the process. Frederick bears much of the responsibility for the partition, for he alone of the monarchs who took part had consciously desired it. Since both Russia and Austria were persuaded to follow a policy that was largely Prussian in inspiration, it ranks as perhaps his greatest diplomatic success.