The mass looting died down as stocks of minerals were depleted, and soldiers were encouraged by their commanders to take part in small-scale looting, which started an "active extraction phase". Natural resources that were not stolen were often purchased with counterfeit Congolese francs, which contributed to inflation. Air transportation companies that once operated in the Congo disappeared and were replaced by companies affiliated with foreign armies. The Congolese government lost tax revenue from natural resources entering or leaving its air fields; air services were controlled by Rwandan and Ugandan troops, who routinely exported coltan from the Congo. The increase in air transportation networks also increased exploitation because of the new transport routes.