Iron in Africa was a great discoever for the early civilizations that lived there, they now had a better weapon making material. The people who had the iron, and made their weapons with it, had more firepower than their enemies. Iron also helped with different things such as cooking utensils, jewelry, and various other things.
In my opinion, the desert would by the hardest place to live because it's so hot and there's hardly any water around. I would hontestly die within five mintues without an A.C. There's also the conflict of sandstorms, not such a pretty thing. I'm not cut out for this style of life, honestly.
Trade helped Islam spread by the Muslim merchants  being able to pass different things on to their customers.
Iman, Salah, Zakah, Sawm, and Hajj are the Five Pillars of Islam. Iman is faith, Salah is prayer, Zakah is donation to charity, Sawm is fasting, and Hajj is the pilgrimage to the Makkah. Sawm is most likely the hardest one because you're hungry all day and want to eat some food, but can't. I'd never make it like that.