The frontier, formed by these two rivers, established between Poland and Soviet-occupied Germany in 1945: it had once marked the frontier of medieval Poland. As a result of an agreement at the Potsdam Conference, nearly one-fifth of Germany’s territory in 1938 was reallocated, mainly to Poland. Germans were expelled from these eastern territories, which were resettled by Poles. The frontier, which became the eastern boundary of the German Democratic Republic, was later accepted by the Federal Republic (West Germany) as part of the policy of détente known as Ostpolitik, and confirmed in 1990 when reunification took place.