Capistrano has meanwhile found an ally in the Polish archbishop Zbigniev Olesniczki, who urges Casimir IV Jagellon, grand duke of Lithuania and king of Poland, to abolish the privileges that had been granted to the Jews in 1447.

In supporting Olesniczki's demand, Capistrano threatens the king, in case of resistance, with horrible sufferings in hell, and predicts great misfortune to the country.

The king at first refuses to comply; but when the Polish army is defeated in September, 1454, at Chojnice in the war with the Teutonic Knights (who are secretly assisted by the pope and the Polish Church), and the clergy announces that God has punished the country because of the king's negligence of the Church and for his protection of the Jews, Casimir yields and revokes the privileges which the latter had enjoyed.

This leads to persecutions of the Jews in many Polish towns.