Answer:
Deserts
Step-by-step explanation:
The deserts were long hot and a good ways from any water sources. This made it hard to travel or trade, usually because it would dry up anyone's water supply that stepped into the scourging heat. Africa created a trade route and water sources along it in order for travel to begin. Also because of modern day airplanes we can now fly over the desert without feeling the scourging sun!
~ LadyBrain