Another of the treaty's important provisions was Germany's confirmation of the by now internationally recognised border with Poland, and other territorial changes in Germany that had taken place since 1945, preventing any future claims to lost territory east of the Oder-Neisse line (see also Former eastern territories of Germany) which had historically been part of Germany for centuries before 31 December 1937. The treaty defined the territory of a 'united Germany' as being the territory of East Germany, West Germany and Berlin, prohibiting Germany from making any future territorial claims. Germany also agreed to sign a separate treaty with Poland reaffirming the present common border, binding under international law, effectively relinquishing these territories to Poland.