Lands of the Bohemian Crown
The river became an internal border, when the Luxembourg king John of Bohemia step-by-step vassalized the Piast dukes of Silesia and incorporated their lands with the consent of King Casimir III of Poland by the 1335 Treaty of Trentschin, whereafter both Lusatia in the west and Silesia in the east became Lands of the Bohemian Crown.