 Soon after the beginning of the Thirty Years' War Bremen declared its neutrality, as did most of the territories in the Lower Saxon Circle.John Frederick, Lutheran Administrator of the Prince-Archbishopric of Bremen, desperately tried to keep his Prince-Archbishopric out of the war, with the complete agreement of the Estates and the city of Bremen.When in 1623 the Republic of the Seven United Netherlands, which was fighting in the Eighty Years' War for its independence against Habsburg's Spanish and imperial forces, requested its Calvinist co-religionist Bremen to join them, the city refused, but started to reinforce its fortifications.