Tropical rainforest, the high mountains and wild rivers were some of the physical obstacles that the Incas faced. They had to build a complex network of roads to link the entire Inca empire. They had messenger stations along these roads so that they could relay their messages, and they built shelters along the way for travelers.
D. Revivalists sent missionaries to convert Americans living in remote regions
Steel. Andrew Carnegie used it to mass produce steel cheaply and efficiency.
