When Władysław's second son Casimir became Duke of Bytom, he at first ruled jointly with his brother Duke Bolko I of Opole and from 1284 on alone. The conflict with his Piast cousin Duke Henryk IV Probus of Silesia-Wrocław led Casimir to seek shelter from King Wenceslaus II of Bohemia and in 1289 he became the first Silesian Piast duke to submit himself under Bohemian overlordship.
With the death of Casimir's grandson Duke Bolesław in 1355 the Bytom branch of the Piasts became extinct and in the following inheritance dispute his widow Margareta of Sternberg had to cede the northern part of the duchy including the lordship of Koźle to Duke Konrad I of Oleśnica, while the remaining part was bequested to Duke Casimir I of Cieszyn. Bytom remained divided until in 1459 Duke Wenceslaus I of Cieszyn sold his portion to Duke Konrad IX the Black of Oleśnica and the duchy was reunited under his rule.
