What is the difference between slavery tolerated because of "necessity" and slavery affirmed as a "moral right"?

Slavery tolerated because of "necessity" means that you do not really want to do it, but you think you must do it. An example is when you have a farm and you need people to work on it. The trouble behind this scenario is that your farm isn’t making money to pay your farm helpers their proper wages, so you resort to slavery. In this case, you do not need money for salaries because your farm is doing well to keep your slaves clothed and fed.

Slavery affirmed as a "moral right" is when you think it is your right to be the master and the slaves deserves to be slaves.

i really really really really really really dont know

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