Marx theorised a changed relation between men and machines. Machines had changed: they had been hooked up to natural energy sources, first steam, then petroleum, then electricity. So men could change too: their work relations and skills could be reorganised. In the Industrial Revolution, labourers acted upon natural materials but only through the mediation of increasingly complex machinic apparatuses, so complex and expensive that, unlike their artisan forebears, industrial workers could not own their own tools. The consequences of these alterations in the daily work life of men and women were played out in the politics and society of the past two centuries and were increasingly the main focus of historical investigations. History took into account a new relation of humans to machines.