During the subsequent Potsdam Conference in July – August 1945 , the three major Allies ratified the colossal westerly shift of Polish borders and approved its new territory between the Oder – Neisse line and Curzon Line . Following the destruction of the Polish-Jewish population in the Holocaust , the flight and expulsion of Germans in the west , resettlement of Ukrainians in the east , and the repatriation of Poles from Kresy , Poland became for the first time in its history an ethnically homogeneous nation-state without prominent minorities . The new government solidified its political power over the next two years , while the Polish United Workers ' Party ( PZPR ) under Bolesław Bierut gained firm control over the country , which would become part of the postwar Soviet sphere of influence in Central and Eastern Europe . The Constitution of the Polish People 's Republic was promulgated in July 1952 and the state officially became the Polish People 's Republic ( PRL )
Potsdam Conference
Potsdam Conference
History of Poland (1945–1989)