[2] When the Second Northern War broke out in 1654, Charles X Gustav of Sweden offered an alliance to Frederick William I, the "Great Elector" of Brandenburg and duke of Prussia.

[5] In Königsberg, the "Great Elector" further had to meet the Swedish demands for Pillau and Memel, promise financial and military aid, and surrender half of the port duties to Sweden.

[7] Sweden offered conquered Polish territories, and Frederick William I went to support Charles X Gustav with his newly formed army in the Battle of Warsaw on 28–30 July, which marked "the beginning of Prussian military history".

[8] Though victorious, the subsequent entry into the war of the Russian tsar, the Holy Roman Emperor and the Dutch navy left Sweden in an unfavourable condition, and dependent on further Brandenburgian support.

[11] A Calvinist himself, he also obliged himself to grant religious freedom to the Lutherans in his Prussian territories, confirming the similar articles IV and XVII of the treaties of Marienburg and Königsberg, respectively.

[7] When an envoy of Ferdinand III, Holy Roman Emperor proposed Polish acceptance of Hohenzollern sovereignty in Prussia in turn for Frederick William I joining the anti-Swedish camp and supporting the Habsburg candidate in the next imperial elections, the "Great Elector" signaled his willingness to change sides.