The Prussian Confederation (German: Preußischer Bund, Polish: Związek Pruski) was an organization formed on 21 February 1440 at Kwidzyn by a group of 53 nobles and clergy and 19 cities in Prussia, to oppose the arbitrariness of the Teutonic Knights. It was based on the basis of an earlier similar organization, the Lizard Union established in 1397 by Chełmno Land nobles.
In 1454, the leader of the Confederation, Johannes von Baysen (Jan Bażyński), formally asked King Casimir IV Jagiellon, to incorporate Prussia into the Kingdom of Poland as a fief. This marked the beginning of the Thirteen Years' War between the Order's State and Poland, with the Prussian cities financing the military costs of the latter.
Read more about Prussian Confederation: Background, Establishment, Thirteen Years' War, Aftermath, Participating Towns