The option that best describes the role of the Sahara in the history of empires in western Africa from the seventh century CE to the sixteenth century CE is:
The Sahara was an important source of natural resources, and facilitated cultural influence through trade systems.
This option accurately reflects how the Sahara served as both a barrier and a facilitator of trade, enabling the exchange of goods, ideas, and cultures, particularly through trans-Saharan trade routes.