In February 1631 "John Frederick" conferred with "Gustavus II Adolphus" and a number of Lower Saxon princes in Leipzig, all of them troubled by Habsburg's growing influence wielded by virtue of the "Edict of Restitution" in a number of Northern German Lutheran prince-bishoprics. "John Frederick" speculated to regain the Prince-Archbishopric of Bremen and therefore in June/July 1631 officially allied himself with Sweden. For the war being "John Frederick" accepted the supreme command of "Gustavus II Adolphus", who promised to restitute the Prince-Archbishopric to its former Administrator. In October an Army, newly recruited by "John Frederick", started to reconquer the Prince-Archbishopric and – supported by Swedish troops – to capture the neighboured Prince-Bishopric of Verden, de facto dismissing "Verden's" Catholic Prince-Bishop Count Francis of Wartenberg (ruled 1630-1631), and causing the flight of the Catholic clergy wherever they arrived. The "Prince-Bishopric of Verden" became subject of a Swedish military administration, while "John Frederick" ascended its See in 1631.