As demand for smartphones, laptops and electric vehicles has soared, so has demand for the minerals - such as cobalt and coltan - for the batteries that power them. The Democratic Republic of the Congo has vast reserves of these minerals, and their extraction is fuelling the country's civil war. Josh Toussaint-Strauss finds out more about how global demand for tech is causing human suffering in central Africa, and how we, and western powers and companies, are complicit