The main way in which a cataract can serve as a natural protective barrier is by reducing the amount of UV radiation that enters the eye from sunlight, which is also why it can lead to blindness, however.
Txting while driving is the greates preventable cause of death my friend
1. West Africa before the Portuguese was a thriving region. There were several kingdoms that were very wealthy, and the main reason for that was that they had lot of natural resources and the trade. These kingdoms were conducting the majority of the trade between Northern Africa and sub-Saharan Africa, so they were able to gain lot of wealth from the countless goods that were traded through their territories.
2. Europe after the Crusades experienced a real ''boom'' in the trade, thus in its economy as well. Through the Crusades, the Europeans were introduced to lot of goods from the Middle East and the rest of Asia. Lot of those goods were very useful or attractive, so the Europeans gradually started to engage in trade with Asia more and more, with the pinnacle of this trade being during the existence of the Mongol Empire.
3. America before Columbus was much more limited when it came to trade and commerce. Unlike the Old World, the civilizations in the New World were engaging into trade only with the civilizations that surrounded them, thus it was more locally or regionally. The majority of the people were still mostly producing goods just about enough to sustain themselves, so they were not engaging into a large scale trade with places further away.
