The breakdown of the wartime alliance made the 1937-borders goal permanently unachievable

Evidence

In a similar vein, the Hallstein Doctrine, which refused diplomatic relations to nations that recognized the GDR, denied the GDR’s legitimacy and reinforced the FRG’s claim to exclusive representation. In fact, neither Adenauer’s pipe dream of colonizing the ‘East’ nor even the ‘modest’ goal of a reunited Germany with its 1937 borders, which no Weimar nationalist would have accepted, was achievable. If the Allies at Potsdam saw the Oder–Neisse boundary as ‘temporary’ pending a final settlement, the breakdown of the ‘Grand Alliance’ ensured the de facto sovereignty of Poland and the Soviet Union over former Prussian territory. — Manuel Borutta and Jan C. Jansen, Vertriebene and Pieds-Noirs in Postwar…, 191