At the 1943 Tehran Conference the allies decided that the new Eastern border of Germany would run along the Oder but after World War II , the Oder and the Lusatian Neisse formed the Oder – Neisse line , which was designated by the victorious allies at the Potsdam Conference as the new border between Poland and Germany . A significant percentage of the German populations east of these two rivers were evacuated by the Nazis or fled before the approaching Red Army . After the war , the remaining population was forcibly expelled in accordance with the Potsdam Agreement . East Germany confirmed the border with Poland in 1950 , then West Germany , after a period of refusal , finally accepted the border in 1970 . In 1990 newly reunified Germany and the Republic of Poland signed a treaty recognizing it as their border
Potsdam Conference
Potsdam Conference
Oder