
Originally Posted by
Londinium
Probably the early 18th century when it was throwing the Ottomans out of Hungary and perfoming handily during the War of the Spanish Successsion. By the middle of the 18th century it began it's long decline when Prussia took Silesia in the war of the Austrian Succession. While it was hardly a rapid decline, from the middle of the 18th until 1918 the Austrian Empire was on a prolonged downward spiral. Prussia began to challenge it within the German lands and France and Britain far outstripped it due to their colonial activities, trade and manufacturing.
Of course you could include the early period of the Habsburg HRE's aswell when the Holy Roman Empire had much more power but Austria as a nation didn't really exist then, it was just the Habsburg family lands.