In June 1945 , the Provisional Government of National Unity was established in Moscow . In July , Bierut and other Polish leaders participated in the Potsdam Conference , where , together with Stalin , they successfully lobbied for the establishment of Poland 's western border at the Oder – Neisse line . Poland 's newly acquired " Recovered Territories " had thus reached their maximal attainable size
Potsdam Conference
Potsdam Conference
Bolesław Bierut