How was slavery that existed in africa different from the transatlantic slave trade?

The fundamental difference between the slave institution in Africa and America or Europe was the issue of treatment and ,rights, and property.

In Africa, slaves were well treated, well fed, and were not mistreated. They were not considered property but were taken for repayment of debts. Their children were not slaves.
In Europe or America, slaves were considered property, without rights and their children and grand children were also slaves. They were mistreated and underfed.