After the 1410 Battle of Grunwald the town was occupied by the united forces of the Grand Duchy of Lithuania and the Kingdom of Poland until 1461. During the Polish–Teutonic Hunger War of 1414, Mohrungen incinerated completely. In 1440, the citizens joined the Prussian Confederation, and after the outbreak of the Thirteen Years' War in 1454, they sided with Poland. At the request of the confederation King Casimir IV Jagiellon signed the act of incorporation of the region to the Kingdom of Poland and on June 11 1454 in Elbing (Elbląg), the town pledged allegiance to the Polish King. The town fought against the Teutonic Order in the war from 1454 to 1466. Reconquered by the Elbing commander Heinrich Reuß von Plauen in 1461, the town became his seat as deputy Grand Master. The command of the town was given to Ertman von Kirchberg, who oppressed the inhabitants. After the peace treaty signed in Toruń in 1466, Mohrungen remained part of the Teutonic state and at the same time came under Polish suzerainty as a fief.