This introductory chapter discusses the consequences of forced migrations for those regions where the established inhabitants were expelled and replaced by new settlers from elsewhere. It particularly studies the city of Wroclaw, the largest city in the German territories ceded to Poland after the war and the largest city ever to experience a total population exchange of this kind. As a large city, Wroclaw is well suited for an investigation of the complex consequences of such a population exchange. Compared to other large Polish cities with a similar history, such as Szczecin and Gdansk, Wroclaw offered decisive advantages. In 1945, Szczecin became a border city, having lost a significant portion of its hinterland as well as its economically crucial connection to Berlin. In Wroclaw, by contrast, established regional relations were preserved because almost all of Silesia became Polish in 1945.