Answer:
Slaves' terms never expired.
The children of slaves had no rights and, therefore, also became slaves.
Slaves cost more than indentured servants, and the high death rate among tobacco workers made it economically unappealing to pay for a lifetime of labor. As a result, for decades, servants from England formed the backbone of the Chesapeake labor force. As the death rate began to fall, it became more economical to purchase a laborer for life.
Slaves were more resistant to epidemics than natives were.
