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1758

In early 1758, Frederick launched an invasion of Moravia and laid siege to Olmütz (now Olomouc, Czech Republic). Following an Austrian victory at the Battle of Domstadtl that wiped out a supply convoy destined for Olmütz, Frederick broke off the siege and withdrew from Moravia. It marked the end of his final attempt to launch a major invasion of Austrian territory. In January 1758, the Russians invaded East Prussia, where the province, almost denuded of troops, put up little opposition. East Prussia had been occupied by Russian forces over the winter and would remain under their control until 1762, although it was far less strategically valuable to Prussia than Brandenburg or Silesia. In any case, Frederick did not see the Russians as an immediate threat and instead entertained hopes of first fighting a decisive battle against Austria that would knock them out of the war.

In April 1758, the British concluded the Anglo-Prussian Convention with Frederick in which they committed to pay him an annual subsidy of £670,000. Britain also dispatched 9,000 troops to reinforce Ferdinand's Hanoverian army, the first British troop commitment on the continent and a reversal in the policy of Pitt. Ferdinand's Hanoverian army, supplemented by some Prussian troops, had succeeded in driving the French from Hanover and Westphalia and re-captured the port of Emden in March 1758 before crossing the Rhine with his own forces, which caused alarm in France. Despite Ferdinand's victory over the French at the Battle of Krefeld and the brief occupation of Düsseldorf, he was compelled by the successful manoeuvering of larger French forces to withdraw across the Rhine.

By this point Frederick was increasingly concerned by the Russian advance from the east and marched to counter it. Just east of the Oder in Brandenburg- Neumark, at the Battle of Zorndorf (now Sarbinowo, Poland), a Prussian army of 35,000 men under Frederick on 25 August 1758, fought a Russian army of 43,000 commanded by Count William Fermor. Both sides suffered heavy casualties—the Prussians 12,800, the Russians 18,000—but the Russians withdrew, and Frederick claimed victory. The American historian Daniel Marston described Zorndorf as a "draw" as both sides were too exhausted and had taken such losses that neither wished to fight another battle with the other. In the undecided Battle of Tornow on 25 September, a Swedish army repulsed six assaults by a Prussian army but did not push on Berlin following the Battle of Fehrbellin.

The war was continuing indecisively when on 14 October Marshal Daun's Austrians surprised the main Prussian army at the Battle of Hochkirch in Saxony. Frederick lost much of his artillery but retreated in good order, helped by dense woods. The Austrians had ultimately made little progress in the campaign in Saxony despite Hochkirch and had failed to achieve a decisive breakthrough. After a thwarted attempt to take Dresden, Daun's troops were forced to withdraw to Austrian territory for the winter, so that Saxony remained under Prussian occupation. At the same time, the Russians failed in an attempt to take Kolberg in Pomerania (now Kołobrzeg, Poland) from the Prussians.

In France, 1758 had been disappointing and in the wake of this, a new chief minister, the Duc de Choiseul, was appointed. Choiseul planned to end the war in 1759 by making strong attacks on Britain and Hanover.