The Ostflucht (flight from the East) was a movement by residents of the former eastern territories of Germany, such as East Prussia, West Prussia, Silesia and Province of Posen beginning around 1850, to the more industrialized western German Rhine and Ruhr provinces. Along with ethnic Germans, many of those migrating to the Ruhr were originally of Polish ethnicity later so-called Ruhrpolen.

America, which had been the major destination of emigrants from the German East, lost much of its attraction when it stopped granting free land to settlers in 1893. At the same time, the Ruhr area prospered, leading to a high demand of workforce, especially in coal mining and heavy industries. This led to an East-to-West inner-Prussian migration. Until 1907, of Prussia's eastern provinces (Pomerania, West Prussia, East Prussia, Posen, Silesia), 2,300,000 emigrated, while only 358,000 migrated into these provinces. Among these were 600,000 were Poles, This loss of workforce hit farms, which made up for this calling in season workers from further east. Berlin and Brandenburg in the same time gained 1,200,000 inhabitants, while the Ruhr area and surrounding provinces (Westphalia and Palatinate) gained 640,000 people.