 Frederick of Prussia 's invasion of Saxony in August 1756 began the Seven Years ' War . Empress Maria Theresa and Kaunitz wished to exit the war with possession of Silesia . Austria was aligned with France and Russia , Great Britain with Prussia and Portugal . Giving Austria huge subsidies came back to haunt France . It could not bolster defences in New France ; the British easily captured Louisbourg in 1758 , and went on to conquer all of New France . 
