Answer:
Force people to work until they die.
Actually the black experience in America was one of the better situations for slaves. While no slavery is good slavery, they were considered valuable property and were well cared for.
To beat a slave was akin to a person buying a new car and trashing it. A foolish and expensive waste of assets. Slaves were taught to read, write and were well cared for. The situation shortly after slavery ended for many blacks was far worse then slavery itself. They lost their homes, jobs, income and even their lives in many cases.
Slavery in Africa today involves a far more severe from of oppression. People are forced to work in intolerable situations with little food or support.
Asian slavery involves, in many cases, prostitution. Children are sold into very poor situations in the hopes they will catch the eye of a richer patron that will care for them.