Historical industrial heartlands have shifted to the right over the past decades, but the sources of this electoral realignment remain difficult to ascertain. We argue that the timing and intensity of industrialization shape contemporary spatial heterogeneities in voting behavior through persistent sociodemographic sorting. To examine our argument, we study the long-term effects of coal mining in Germany's Ruhr area. We match the geolocation of 1,000 mining shafts and historical plant-level employment surveys with electoral outcomes at the neighborhood level. For identification, we exploit the varying depths of coal deposits that governed the adoption of deep-shaft mining. We show that communities that industrialized later and more intensively exhibit higher support for the radical right and social democrats today, coupled with lower turnout. These effects are driven by the consequences of intensive industrialization for neighborhood sorting and long-term economic performance: Historical mining communities are significantly poorer and more socioculturally diverse today than communities with less intensive industrialization experiences. Using rich historical census data, we demonstrate that these structural differences did not exist prior to industrialization. We also consider the role of historical migration waves into the Ruhr area, showing that greater demographic upheaval due to labor migrants from Prussia's Eastern frontier is associated with lower incomes in the present. Finally, we exploit the quasi-random settlement distribution of migrant groups with different confessional alignments to examine the second-order effects of specialization in coal mining. This paper contributes to our understanding of how the path of development influences cleavage formation in the long run.