Fürstbistum Ermland
Frederick William, Duke of Prussia and Prince-elector of Brandenburg, sought to acquire Royal Prussia in order to territorially connect his two existing fiefs. An opportunity occurred when Charles X Gustav of Sweden, in his attempt to conquer Poland (cf. Swedish Deluge), promised to cede to Frederick William the Polish-Prussian voivodeships of Chełmno, Malbork and Pomerania as well as the Prince-Bishopric of Warmia, if Frederick William supported the Swedish campaign. This offer was speculative since Frederick William would have to commit to military support of the campaign, while the reward was conditional on achieving victory.