This is the second installment of Kulczycki's examination of the Polish working-class diaspora in the Ruhr Valley, the coal-rich region in the west that, like Upper Silesia in the southeast, belonged to Prussia. Both the Ruhr and Upper Silesia contained significant Polish populations. Coal mining and steel production in these two regions fueled first Prussia's and then, after 1871, Imperial Germany's rise as a Great Power. Mention of “the Polish-German antagonism” will invariably bring to mind the tense history of Polish–German diplomatic relations leading up to the outbreak of World War Two and the ensuing apocalypse. The post-1918 border conflicts between Germany and Poland, especially the bloody struggle in Upper Silesia, might also come up. Depending on the audience, the roughly four million Prussian Poles in Poznania and Western Prussia could also receive attention. However, it is unlikely that the Polish population in the Ruhr would be recognized, at least on this side of the Atlantic, as a distinct group with its own chapter in the history of Polish–German relations. Yet in 1914 there were roughly one hundred thousand Polish miners in the Ruhr, comprising about a quarter of the work force.