Why do you think the word Slavery is never mentioned in the Consitution?

All three clauses referred to slaves as "Persons" and not property. Also, the fact that the word "slave" was never written in the Constitution demonstrated that slavery was not accepted by all the Framers, and they hoped it would be eliminated.

Explanation:

the answer should be monarchy

these civilizations were located around fertile rivers, where they could produce an abundance of crops