The Ostflucht reference article from the English Wikipedia on 24-Jul-2004
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Ostflucht

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The Ostflucht (east flight) was the movement of the German population of East Prussia, West Prussia, Silesia and Province of Posen beginning around 1850, to the more industrialized Rhine and Ruhr provinces. At the same time massive movements of neighboring Russia-Poles going westwards into Prussia/Germany caused imbalances and upheavals. The loss of Germans and the higher Polish birth rate in these areas caused concern among German nationalists. The result was special laws: