Recovered or Regained Territories (Polish: Ziemie Odzyskane, literally ""Regained Lands"") was an official term used by the People's Republic of Poland to describe the territory of the former Free City of Danzig and the parts of pre-war Germany that became part of Poland after World War II. The rationale for the term ""Recovered"" was the Piast Concept that these territories were once part of the traditional Polish homeland. They had been part of, or fiefs of, a Polish state during the medieval Piast dynasty. Over the centuries, however, they had become Germanized through the processes of German eastward settlement (Ostsiedlung) and political expansion (Drang nach Osten) and for the most part did not even contain a Polish-speaking minority.The great majority of the German inhabitants either fled or were expelled from the territories during the later stages of the war and after the war ended, although a small German minority remains in some places. The territories were resettled by the Polish communist government, mainly with Poles who moved voluntarily from Central Poland and the wartime Polish diaspora, but also with some Ukrainians, Rusyns and other minorities forcibly resettled under ""Operation Vistula,"" as well as Polish ""repatriates"" forced to move from areas of former eastern Poland that were annexed by the Soviet Union. The communist authorities also made efforts to remove many traces of German culture, such as place names and historic inscriptions on buildings, from the territories.The post-war border between Germany and Poland (the Oder-Neisse line) was formally recognized by East Germany in 1950 and by West Germany in 1970, and was affirmed by the re-united Germany in the German-Polish Border Treaty of 1990.