didn't last long, because in the Danish-Swedish Torstenson War of 1643–1645 the Swedes seized de facto rule in both prince-bishoprics. Christian IV of Denmark and Norway had to sign the Second Peace of Brömsebro on 13 August 1645, and a number of Danish territories, including the two Swedish occupied prince-bishoprics, were ceded into Swedish hands. So Frederick II had to resign as Administrator in both prince-bishoprics. He succeeded his late father on the Danish throne as Frederick III of Denmark in 1648. With the impending enfeoffment of the military great power of Sweden with the Prince-Archbishopric of Bremen, as under negotiation for the Treaty of Westphalia, the city of Bremen feared falling under Swedish rule as well. Therefore, the city beseeched an imperial confirmation of its status of imperial immediacy from 1186 (). In 1646 Emperor Ferdinand III granted the Free Imperial City of Bremen the requested confirmation (). Transformation of prince-bishoprics into Bremen-Verden in 1648 The political entities of the Prince-Archbishopric of Bremen and the Prince-Bishopric of Verden were transformed by the Peace of Westphalia in 1648 into the Duchy of Bremen and the Principality of Verden, however, colloquially the Duchies of Bremen and Verden, without changing the territories' status of imperial immediacy and imperial estate. Every imperial estate, thus Bremen and Verden separately, was represented in the Diet () of the Holy Roman Empire. The formerly Free Imperial City of Verden upon Aller was mediatised by the Peace of Westphalia and incorporated into the Duchy of Verden. The two neighbouring territories could not unite in a real union without finding support by the emperor and a majority among the imperial estates, which never happened. They were parts of two different imperial circles. From 1500 on the Prince-Archbishopric of Bremen and thus its successor Duchy of Bremen belonged to the Saxon Circle (later the Lower Saxon Circle; ), a fiscal and military substructure of the Empire. The Prince-Bishopric of Verden and thus its successor, the Duchy of Verden, on the other hand, belonged to the Lower Rhenish-Westphalian Circle (, colloquially Westphalian Circle). The Holy Roman Empire's taxes were collected and armies recruited and financed along the lines of the imperial circles. Bremen and Verden sent their representatives to the circle diet (Kreistag) of their respective imperial circle. The circle diet decided how to share the burden of the taxes to be levied among the member territories. Thus Bremen and