This mine feeds the tech world and fuels a rebel war

Under the watchful eye of M23 rebels in the hills around the Congolese town of Rubaya, a line of men in rubber boots ferry sacks full of crushed rocks up winding paths cut into the slopes. The laborers are hauling coltan ore, a mineral that powers the modern world. The ore will be loaded onto motorbikes and eventually shipped thousands of kilometers away to Asia. There it’s processed into tantalum, a heat-resistant metal that fetches more than $300 a kilogram and is in high demand by...