Oder-Neisse line, frontier established in 1945 between Germany and Poland; it followed the Oder and W Neisse rivers from the Baltic Sea to the Czechoslovak border. The boundary, desired by most Poles at the expense of Germany, came about as a result of agreements between the Soviet Union, Great Britain, and the United States at the Yalta and Potsdam conferences in 1945. The Soviet leader Joseph Stalin endorsed the Oder-Neisse line partly as a compensation for the Polish eastern territories that the USSR had annexed and partly under pressure from the USSR-sponsored Polish government. Although the boundary was originally opposed by the United States and Great Britain because it would make Poland excessively dependent upon the Soviet Union, they sanctioned it informally at Yalta in Feb., 1945. After disputed territories, including the former free city of Danzig (now Gdansk), had been in effect incorporated into Poland and their German population largely expelled, the Potsdam Conference of Aug., 1945, recognized the line as Poland's western frontier pending a peace treaty with Germany. In the absence of such a treaty, an agreement between the German Democratic Republic (East Germany) and Poland recognized the line as the permanent frontier in 1950. The West German government recognized it in 1971. In 1990, during negotiations for German reunification, the East and West German legislatures agreed to recognize the inviolability of the Polish-German border, much to the relief of neighboring states.