The nature of the "de facto" collectively ruled governance of Brandenburg-Prussia became more apparent through the titles of the higher ranks of the Prussian government, seated in Brandenburg's capital of Berlin after the return of the court from Königsberg, where they had sought refuge from the Thirty Years' War (1618–1648). However, the legal amalgamation of the Kingdom of Prussia (a sovereign state) with Brandenburg (a fief of the Holy Roman Empire) was achieved only after the dissolution of the Empire in 1806 during the Napoleonic Wars.