Both Lusatias formed separate Bohemian crown lands under the rule of the Luxembourg , Jagiellon and — from 1526 — Habsburg dynasties . In the course of the Reformation the vast majority of the population turned Protestant . The Bohemian era came to an end when Emperor Ferdinand II of Habsburg ceded the Lusatias to Elector John George I of Saxony under the 1635 Peace of Prague in return for his support in the Thirty Years ' War ; thus the lands returned to the House of Wettin . As the Kingdom of Saxony had sided with Napoleon it had to cede Lower Lusatia to Prussia in the 1815 Congress of Vienna , whereafter the territory became part of the Province of Brandenburg . With the implementation of the Oder – Neisse line by the 1945 Potsdam Conference , the lands east of the Neisse river fell to Poland
Potsdam Conference
Potsdam Conference
Lower Lusatia