text: In 1756, Frederick attempted to forestall Britain's financing of a Russian army on Prussia's border by negotiating an alliance with Britain at the Convention of Westminster, by which Prussia would protect Hanover against French attack, and Britain would no longer subsidise Russia. This treaty triggered the Diplomatic Revolution in which Habsburg Austria and Bourbon France, who had been traditional enemies, allied together with Russia to defeat the Anglo-Prussian coalition. To strengthen his strategic position against this coalition, on 29 August 1756, Frederick's well-prepared army preemptively invaded Saxony. His invasion triggered the Third Silesian War and the larger Seven Years' War, both of which lasted until 1763. He quickly captured Dresden, besieged the trapped Saxon army in Pirna, and continued marching the remainder of his army toward North Bohemia, intending to winter there. At the Battle of Lobositz he claimed a close victory against an Austrian army that was aiming to relieve Pirna, but afterward withdrew his forces back to Saxony for the winter. When the Saxon forces in Pirna finally capitulated in October 1756, Frederick forcibly incorporated them into his own army. This action, along with his initial invasion of neutral Saxony, brought him widespread international criticism; but the conquest of Saxony provided him with significant financial, military, and strategic assets to sustain the war.
  In the early spring of 1757, Frederick again invaded Bohemia. He was victorious against the Austrian army at the Battle of Prague on 6 May 1757, but his losses were so great he was unable to take the city, and settled for besieging it. On 18 June 1757, Frederick suffered his first major defeat at the Battle of Kolín, which forced him to abandon his invasion of Bohemia. When the French and the Austrians pursued him into Saxony and Silesia in the fall of 1757, Frederick defeated and repulsed a much larger Franco-Austrian army at the Battle of Rossbach and another Austrian army at the Battle of Leuthen. Frederick hoped these two victories would force Austria to negotiate, but Maria Theresa was determined not to make peace until she had recovered Silesia. Despite its strong performance, the losses suffered from combat, disease and desertion had severely reduced the quality of the Prussian army.