century. In 1885, there were 175 injuries per thousand workers per year. Deaths were low in most years 2 per 1000 workers), but major disaster was always a threat. 1099 men died in the Courrières mine disaster of 1906. The campaign for mine safety enabled miners to break from their peasant psychology and create solidarity that came from sharing dangerous work, and to develop a working-class consciousness. Unions gain strength by setting up a system of worker elected mine-safety delegates. The national government encouraged the mine safety movement as a means of limiting strife in the sometimes turbulent coal fields. Nevertheless, strikes remained very common, and coal miners took the lead in political organization. Germany seized control of some mining districts in the First World War, leaving them devastated. Polish, Spanish and other immigrants were brought in to provide a stable labor force at the end of the war. Germany The first important mines appeared in the 1750s, in the valleys of the rivers Ruhr, Inde and Wurm where coal seams outcropped and horizontal adit mining was possible. In 1782 the Krupp family began operations near Essen. After 1815 entrepreneurs in the Ruhr Area, which then became part of Prussia took advantage of the tariff zone (Zollverein) to open new mines and associated iron smelters. New railways were built by British engineers around 1850. Numerous small industrial centres sprang up, focused on ironworks, using local coal. The iron and steel works typically bought mines, and erected coking ovens to supply their own requirements in coke and gas. These integrated coal-iron firms ("Huettenzechen") became numerous after 1854; after 1900 they became mixed firms called "Konzern." The average output of a mine in 1850 was about ; its employment about 64. By 1900, the average mine's output had risen to and the employment to about 1,400. Total Ruhr coal output rose from in 1850 to 22() in 1880, 60() in 1900, and 114() in 1913, on the verge of war. In 1932 output was down to , growing to 130() in 1940. Output peaked in 1957 (at 123 million()), declining to in 1974. At the end of 2010 five coal mines were producing in Germany. The last hard coal mine in Germany closed on December 21, 2018. The miners in the Ruhr region were divided by ethnicity (with Germans and Poles) and religion (Protestants and Catholics). Mobility in and out of the