Another form of Germanisation of Poles was the relation between the German state and Polish coal miners in the Ruhr Area. Due to migration within the German Empire, an enormous stream of Polish nationals (as many as 350,000) made their way to the Ruhr in the late 19th century, where they worked in the coal and iron industries. Because of the various uprisings in occupied Poland during the previous century, German authorities viewed them as potential danger and a threat and as a "suspected political and national" element.