The Seven Years’ War involved nearly all the European powers and was ignited in 1756 when the Prussian ruler, Frederick II, invaded Holy Roman Empire territories (European territories dominated by Austria) in Saxony. Frederick II wanted to protect his borders from a feared Austro-Russian attack, and believed that Saxony would be the perfect buffer zone. Austria was determined to reclaim Silesia, annexed earlier by the Prussians, and responded immediately to the Saxon incursion, seeing it as hostile and expansionist. The Austrian-led Holy Roman Empire, supported by Spain, Russia, France and Sweden, declared war on the Prussian alliance, which now included Britain and the Hanoverians. Frederick II was mostly successful in his Saxony campaigns and, in 1757, advanced on Prague where he secured a victory, only to be defeated at Kolin. After a series of campaigns, some of which played out on the global stage and spread to India and the North American colonies, the European theatre ended in stalemate; both sides were left impoverished with no significant changes in their European borders.
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