Ruhrpolen (“Ruhr Poles”) is a German umbrella term for Poles (including Silesians, Masurians, Kashubians), who migrated to the rapidly-industrializing areas of the Ruhr Valley, mainly from former eastern territories of Germany (the Prussian provinces of Posen, Silesia, and East and West Prussia.) This migration wave, known as the Ostflucht, began in the late 19th century, with most of the the Ruhrpolen arriving around the 1870s. The migrants found employment in the mining, steel and construction industries. In modern times it is estimated that roughly 150,000 inhabitants of the Ruhr Area (out of roughly 5 million) are of Polish descent.