Ostprovinzen

Ostprovinzen, literally "Eastern Provinces," is a historical designation used predominantly for the eastern territories of the Kingdom of Prussia and later the Free State of Prussia within the German Reich. The term most often refers to the eastern Prussian provinces: Ostpreußen (East Prussia), Westpreußen (West Prussia), and the Province of Posen (Posen), with the composition changing over time as borders and administrative structures evolved. These provinces formed the eastern half of Prussia’s imperial and royal administration and played a central role in German–Polish relations during the 19th and early 20th centuries.

Following World War I, the Treaty of Versailles and subsequent border changes led to large parts of Westpreußen and Posen being ceded to the Second Polish Republic, creating new borders such as the Polish Corridor that separated East Prussia from the rest of Germany. East Prussia remained a German province after the war, though the surrounding shifts intensified the region’s isolation from the German mainland.

In 1945, the redrawing of Europe’s borders after World War II resulted in most of the eastern territories being assigned to Poland or the Soviet Union. The northern part of East Prussia became the Soviet Kaliningrad Oblast, while other areas were incorporated into Poland as new administrative regions; the German provinces themselves ceased to exist as distinct entities. Today, Ostprovinzen is primarily used in historical contexts to describe these former eastern German provinces and their demographic and political significance during the late 19th and early 20th centuries.