After World War II , Poland lost 77,000 km ² of eastern regions ( Kresy ) , gaining instead the smaller but much more industrialized so-called " Regained Territories " east of the Oder-Neisse line . This annexation of German territory was agreed by the Allied Powers at the Potsdam Conference in 1945
Potsdam Conference
Potsdam Conference
Subdivisions of the Polish People's Republic