During the war, Bierut was an activist of the newly founded Polish Workers' Party (PPR) and subsequently the chairman of the State National Council (KRN), established by the PPR. As the Red Army pushed the Nazi Wehrmacht from eastern Poland, liberated Lublin was made the temporary headquarters of the Polish Committee of National Liberation at his initiative. Trusted by Joseph Stalin, Bierut participated in the Potsdam Conference, where he successfully lobbied for the establishment of Poland's western border at the Oder–Neisse line. The conference thus granted Poland the post-German "Recovered Territories" at their maximum possible extent.