sentences:  Unfortunately, King Casimir IV also put his claims over the lands, under the excuse of being the Polish sovereign they had to reverted to the crown.He soon occupied Belz, Rawa Mazowiecka and Gostynin, who were formally added to the kingdom; however, the Thirteen Years' War and the fear of an intervention of the Teutonic Knights, united with the disapproval of the Masovian nobility over the too aggressive politics of the Casimir IV, forced him to accept temporarily the rule of Konrad III over Płock, Płońsk and Zawkrze —although the major support of Konrad III was Princess Catherine of Płock, aunt of the late dukes, whose energetic attitude played a major part in the conflict.The formal recognition of Konrad III as Duke of Płock, however, didn't end his struggle with the Polish kingdom for this land.