[3] In 1655, the rapid progress of the Swedish campaign in Poland–Lithuania made Brandenburgian elector Frederick William I worried about his Duchy of Prussia,[4] which he held as a Polish fief.

[8] Still a vassal of Charles X Gustav for Prussia,[2] Frederick William I entered the war and the combined Swedish-Brandenburgian forces defeated the Polish army in the Battle of Warsaw in July.

[9] This made the Polish king John II Casimir Vasa, from whom Frederick William I had to take Prussia as a fief prior to Königsberg, say that once the Tartars had the Swedes for breakfeast, he would arrest the elector "where neither sun nor moon will shine".

[10] Thirteen towns and 250 villages were burned until Gosiewski was expelled in October, and the campaign was terrifying enough to persist in local folklore until the 20th century.

[12] In the subsequent treaties of Wehlau and Bromberg, John II Casimir confirmed Frederick William I's sovereignty in Prussia after the latter abandoned Sweden in the war.