The communist German Democratic Republic was established in the historic "Mitteldeutschland" ( Middle Germany ). Former German territories east of the Oder and Neisse rivers, mainly the Prussian provinces of Pomerania , East Prussia , West Prussia , Upper Silesia , Lower Silesia , the eastern Neumark of Brandenburg , and a small piece of Saxony were thus detached from Germany. To compensate Poland for the USSR's annexation of its eastern provinces, the Allies provisionally established Poland's post-war western border at the Oder–Neisse line at the Yalta Conference (1945). As a result, most of Germany's central territories became the Sowjetische Besatzungszone (SBZ, Soviet Occupation Zone). All other lands east of the Oder–Neisse line were put under Polish administration, with the exception of historic northern East Prussia , which went to the USSR. 
In the 1772 First Partition of Poland , the Prussian king Frederick the Great annexed neighboring Royal Prussia , ., the Polish voivodeships of Pomerania ( Gdańsk Pomerania or Pomerelia ), Malbork , Chełmno and the Prince-Bishopric of Warmia , thereby connecting his Prussian and Farther Pomeranian lands and cutting the rest of from the Baltic Coast. The territory of Warmia was incorporated into the lands of former Ducal Prussia, which, by administrative deed of 31 January 1773 were named East Prussia . The former Polish Pomerelian lands beyond the Vistula River together with Malbork and Chełmno Land formed the Province of West Prussia with its capital at Marienwerder (Kwidzyn). The Polish Partition Sejm ratified the cession on 30 September 1773, whereafter Frederick officially went on to call himself a King "of" Prussia.