This is actually a misconception. If antebellum Southerners had followed Israel's law, slavery not only would not have existed but would have been treated as a capital offence.
Regarding kidnapping and slavery please view the following texts from the Torah,
"He who kidnaps a man, whether he sells him or he is found in his possession, shall surely be put to death.
"If a man is caught kidnapping any of his countrymen of the sons of Israel, and he deals with him violently or sells him, then that thief shall die; so you shall purge the evil from among you."
This demonstrates that slavery was not the same as the kind we saw in the 19th century antebellum south (there were northerners involved in the trade too for those sensitive to historical accuracy). At that time, trademen went to Africa, kidnapped people and brought them home to sell them to the highest bidder. Again, according to these passages, such a practice would be a capital crime in the Old Testament. Instead, persons who were slaves were usually indentured servants paying off a debt; a resident employee who temporarily was living in the employees' household to work off his debt to him. Sometimes it was for other reasons such as when financial disaster hit a particular household, the family would often sell themselves into service to help pay the bills. This clearly is not the type of slavery we usually think of today. The ‘slavery’ mentioned in the Old Testament was really indentured servant hood and was a very different kind of institution than the New World slavery that developed in modern times.
Consider the following observations made by Paul Copan:
Hebrew Servanthood as Indentured Servitude
We should compare Hebrew debt-servanthood (many translations render this “slavery”) more fairly to apprentice-like positions to pay off debts -- much like the indentured servitude during America’s founding when people worked for approximately 7 years to pay off the debt for their passage to the New World. Then they became free.
In most cases, servanthood was more like a live-in employee, temporarily embedded within the employer’s household. Even today, teams trade sports players to another team that has an owner, and these players belong to a franchise. This language hardly suggests slavery, but rather a formal contractual agreement to be fulfilled -- like in the Old Testament.
Through failed crops or other disasters, debt tended to come to families, not just individuals. One could voluntarily enter into a contractual agreement ("sell" himself) to work in the household of another: “one of your countrymen becomes poor and sells himself” (Leviticus 25:47). A wife or children could be “sold” to help sustain the family through economically unbearable times -- unless kinfolk “redeemed” them (payed their debt). They would be debt-servants for 6 years. A family might need to mortgage their land until the year of Jubilee every 50 years.
Note: In the Old Testament, outsiders did not impose servanthood - as in the antebellum South. Masters could hire servants "from year to year" and were not to “rule over … [them] ruthlessly” (Leviticus 25:46,53). Rather than being excluded from Israelite society, servants were thoroughly embedded within Israelite homes.
The Old Testament prohibited unavoidable lifelong servanthood -- unless someone loved his master and wanted to attach himself to him (Exodus 21:5). Masters were to grant their servants release every seventh year with all debts forgiven (Leviticus 25:35--43). A slave’s legal status was unique in the ancient Near East (ANE) -- a dramatic improvement over ANE law codes: “Hebrew has no vocabulary of slavery, only of servanthood.”
An Israelite servant’s guaranteed eventual release within 7 years was a control or regulation to prevent the abuse and institutionalizing of such positions. The release-year reminded the Israelites that poverty-induced servanthood was not an ideal social arrangement. On the other hand, servanthood existed in Israel precisely because poverty existed: no poverty, no servants in Israel. And if servants lived in Israel, this was voluntary (typically poverty-induced) -- not forced.
The Dignity of Servants in Israel
Israel’s servant laws were concerned about controlling or regulating -- not idealizing -- an inferior work arrangement. Israelites entered into servitude voluntarily -- though not optimal. The intent of Israel’s laws was to combat potential abuses, not to institutionalize servitude. The Old Testament punished forced slavery by death. Once a master freed a person from his servant obligations, the former servant had the “status of full and unencumbered citizenship.”
Old Testament legislation sought to prevent voluntary debt-servitude. God gave Mosaic legislation to prevent the poor from entering, even temporarily, into voluntary indentured service. The poor could glean the edges of fields or pick lingering fruit on trees after their fellow Israelites’ harvest (Leviticus 19:9,10; 23:22; Deuteronomy 24:20,21; cp. Exodus 23:10). Also, God commanded fellow-Israelites to lend freely to the poor (Deuteronomy 15:7,8), and to not charge them interest (Exodus 22:25; Leviticus 25:36,37). And when the poor could not afford sacrificial animals, they could sacrifice smaller, less-expensive ones (Leviticus 5:7,11). Also, people were to automatically cancel debts every 7 years. And when a master released his debt-servants, he was to generously provide for them -- without a “grudging heart” (Deuteronomy 15:10). The bottom line: God did not want there to be any poverty (or servanthood) in Israel (Deuteronomy 15:4). So, servant laws existed to help the poor, not harm them or keep them down.
Rather than relegating treatment of servants ("slaves") to the end of the law code (commonly done in other ANE law codes), the matter is front-and-center in Exodus 21. For the first time in the ANE, God’s legislation required treating servants ("slaves") as persons, not property. Genesis 1:26,27 affirms that all humans are God’s image-bearers. Job states that master and slave alike come from the mother’s womb and are ultimately equals (Job 31:13-15). As one scholar writes: “We have in the Bible the first appeals in world literature to treat slaves as human beings for their own sake and not just in the interests of their masters.”
Three Remarkable Provisions in Israel
A simple comparison of Israel’s law code with those of the rest of the ANE reveal three remarkable differences. If Bible-believing Southerners had followed these three provisions, antebellum slavery would not have existed or been much of an issue.
1. Anti-Harm Laws: One marked improvement of Israel’s laws over other ANE law codes is the release of injured servants (Exodus 21:26,27). When an employer ("master") accidentally gouged out the eye or knocked out the tooth of his male or female servant/employee, he/she was to go free. God did not allow physical abuse of servants. If an employer’s disciplining his servant resulted in immediate death, that employer ("master") was to be put to death for murder (Exodus 21:20) -- unlike other ANE codes.10 In fact, Babylon’s Hammurabi’s Code permitted the master to cut off his disobedient slave’s ear (282). Typically in ANE law codes, masters -- not slaves -- were merely financially compensated. The Mosaic Law, however, held masters to legal account for their treatment of their own servants -- not simply another person’s servants.
2. Anti-Kidnapping Laws: Another unique feature of the Mosaic Law is its condemnation of kidnapping a person to sell as a slave -- an act punishable by death (Exodus 21:16; cp. Deuteronomy 24:7). Kidnapping, of course, is how slavery in the antebellum South could get off the ground.
3. Anti-Return Laws: Unlike the antebellum South, Israel was to offer safe harbor to foreign runaway slaves (Deuteronomy 23:15,16) — a marked contrast to the Southern states’ Fugitive Slave Law. Hammurabi’s Code demanded the death penalty for those helping runaway slaves (16). In other less-severe cases — in the Lipit-Ishtar (12), Eshunna (49-50), and Hittite laws (24) — fines were exacted for sheltering fugitive slaves. Some claim that this is an improvement. Well, sort of. In these “improved” scenarios, the slave was still just property; the ANE extradition arrangements still required that the slave be returned his master. And not only this, the slave was going back to the harsh conditions that prompted him to run away in the first place.11 Even upgraded laws in first millennium BC Babylon included compensation to the owner (or perhaps something more severe) for harboring a runaway slave. Yet the returned slaves themselves were disfigured, including slitting ears and branding.12 This isn’t the kind of improvement to publicize too widely.
Old Testament scholar Christopher Wright observes: "No other ancient near Eastern law has been found that holds a master to account for the treatment of his own slaves (as distinct from injury done to the slave of another master), and the otherwise universal law regarding runaway slaves was that they must be sent back, with severe penalties for those who failed to comply."
If the South had followed these three clear laws from Exodus and Deuteronomy, slavery would have been a nonissue. What’s more, Israel’s treatment of servants ("slaves") was unparalleled in the ANE.
So let's be careful and historically accurate when attempting to equate the African slave trade to the forms of slavery and servant hood you hear about in the Bible. We still have slavery today and it takes place in the prisons. People pay a debt they owe society there.
Lastly, it is good to remember that the Israelites themselves were slaves of the Egyptians for 400 years and God delivered them, bringing judgment on all of Egypt for this oppression. God hates it, and so God delivering His people from the bonds of slavery is one of the key themes of Scripture, and the Exodus points us to Christ who sets us free from bondage.