Between 13 July and 15 August 1391, while Vladislaus II was in Hungary, forces aligned with Władysław II Jagiełło had besieged Kruszwica Castle and later had taken the stronghold in Racibórz, both of which belonged to Vladislaus. By doing so, they had started the war between two monarchs. In September 1391, Jagiełło's forces had captured lands of Gniewkowo Land and Dobrzyń. On 15 September 1391, Jagiełło's forces had entered Wieluń, beginning the war theatre on the territories of the duchy. In the autumn of 1391, the war had ended with Jagiełło's victory. Following that, Duchy of Wieluń was incorporated into Kingdom of Poland.[1][5][6]