Habsburg Austria and Bourbon France, traditional enemies, allied together in the Diplomatic Revolution of 1756 following the collapse of the Anglo-Austrian Alliance. Frederick swiftly made an alliance with Great Britain at the Convention of Westminster. When the neighboring countries began conspiring against him, Frederick determined to strike first. On 29 August 1756, his well-prepared army preemptively invaded Saxony, beginning the Third Silesian War and the larger Seven Years' War, both of which lasted until 1763. He faced widespread criticism for his attack on neutral Saxony and his forcible incorporation of the Saxon forces into the Prussian army following the Siege of Pirna in October 1756. While the Prussian invasion of Saxony was successful, it took uncharacteristically long to complete, costing Prussia the initiative. Frederick's subsequent 1757 invasion of Austrian Bohemia, though initially successful, ended in his first defeat at the Battle of Kolin and forced him into retreat. However, when the French and the Austrians pursued him into Saxony and Silesia, Frederick decisively defeated them at the battles of Rossbach and Leuthen. Frederick hoped these two great victories would force Austria to negotiate, but Maria Theresa was determined not to make peace until she had recovered Silesia, and the war continued. Despite its excellent performance, the Prussian army became increasingly stretched thin by various costly battles.