German eastern territories of the former German eastern territories 1871-1945

Prussia (green) within the German Empire (1871-1918) At the time of the formation of the German Empire in 1871, Prussia was the largest and dominant part of the Empire. As such, the territories of East Brandenburg, Silesia, Pomerania, the Province of Prussia, and Posen became the initial territories within the territories that made up the German Empire. Later, these territories became known as the eastern territories of the German Empire (Ostgebiete des deutschen Reiches).

In some places, such as Posen and southern Upper Silesia, the majority of the population was Polish, while other areas were overwhelmingly German. The intermingling of Germans and Poles gave rise to a debate about whether the territories should belong to Germany or Poland, which lasted at least three-quarters of a century before World War II. After World War II, under the Potsdam Agreement, agreed between July 13 and August 2, 1945, sovereignty over all areas east of the Oder-Neisse line, whether recognized by the international community as German territory or occupied by Germany in World War II, was given to the other countries.