As Chancellor (1753–92) he controlled foreign policy under Empress Maria Theresa and Emperor Joseph II. He was convinced that Prussia was Austria’s most dangerous enemy and his main diplomatic feat was to reverse (1756–57) long-standing European alliances, but Britain remained opposed to France and Austria stayed allied to Russia. However, when Britain formed an alliance with its former enemy, Prussia, in order to protect Hanover, Kaunitz negotiated an alliance with France, thus isolating Prussia on the Continent. Although the ambitions of Frederick II (the Great) were not fully checked, Kaunitz was a leading negotiator of the Treaty of Paris (1763).