Seven Years' War
Frederick saw Saxony and Polish west Prussia as potential fields for expansion but could not expect French support if he started an aggressive war for them. If he joined the French against the British in the hope of annexing Hanover, he might fall victim to an Austro-Russian attack. The hereditary elector of Saxony, Augustus III, was also elective King of Poland as Augustus III, but the two territories were physically separated by Brandenburg and Silesia. Neither state could pose as a great power. Saxony was merely a buffer between Prussia and Austrian Bohemia, whereas Poland, despite its union with the ancient lands of Lithuania, was prey to pro-French and pro-Russian factions. A Prussian scheme for compensating Frederick Augustus with Bohemia in exchange for Saxony obviously presupposed further spoliation of Austria.
What was his concern about trying take Hanover from the British?
he might fall victim to an Austro-Russian attack
If he joined the French against the British in the hope of annexing Hanover, he might fall victim to an Austro-Russian attack.
the British