Duke of Gniewkowo, Władysław the White, had later briefly re-established the duchy in the rebellion fought between 1373 and 1374 and later between 1375 and 1377, and eventually given up his claims to the land in 1377.

Its territories were given to Kazimierz III of Gniewkowo by his father, Ziemomysł of Kuyavia, Duke of Inowrocław, in his testament.

In 1343, according to the Treaty of Kalisz, territories of the duchy were returned to Polish control, and Kazimierz III was reestablished as its ruler.

As Gniewkowo got burned down during the war, Szarlej become the seat of the duke, and therefore, de facto capital of the state.

[3][5][6] This decision probably was caused by the worsening relations with the king of Poland, who, during the border dispute between the duke and the Kuyavian judge Kiwała, ruled in favour of the latter.

[3][5] Władysław, supported by Ulrich von Osten and a few Burgundian military units of Philip the Bold, had invaded Kuyavia again in 1375.

[10][5][6] In March 1377, in the agreement signed in Brześć Kujawski, Władysław the White agreed to give up his claims to the throne of Poland and lands of the Duchy of Gniewkowo.