I also believe the use of slaves in the Bible is what we would now refer to as indentured servants.
Allow me to correct myself.
I also believe the use of slaves in the Bible is what we would SOMETIMES refer to as indentured servants.
The Old Testament economy permitted the use of conquered peoples as chattel or near-chattel slaves rather than killing them, under some circumstances.
The New Testament concept (under the Roman Empire) was closer to the modern indentured servant, who retained the right to purchase his or her own freedom.