Parallel structure should be used when you connect clauses with a coordinating conjunction such as: for, and, nor, or, but, so, or yet. Some examples of this include: Correct: Every morning, we make our bed, eat breakfast and feed the dog. Incorrect: Every morning, we make our bed, eating breakfast and feed the dog.
Either, Meroe became very involved in nation trade, or, traders from other lands traveled the Nile to exhchange goods.