History tells us many American preachers during the days leading up to our Civil War justified slavery based upon passages such as I Peter 2:18 which tell servants to be subject to their masters. But perhaps these preachers were overlooking the fact that there are at least two types of slaves described in the Bible. One is forced slavery such as we saw in America two or three centuries ago. The other we call an indentured servant. That is when a man voluntarily (or through court order) sells/rents himself into slavery in order to pay off a large debt that he couldn’t pay off otherwise.
The former type was sometimes authorized in the old testament when the Israelites were allowed to take prisoners as slaves when they won wars against foreign national enemies. But this type is never allowed in the new testament and is specifically condemned in passages like I Timothy 1:10 which condemns “menstealers” (“enslavers” – ESV, “slave traders” – NIV). The old testament allowed (even commanded) the Israelites to “hate your enemies” (Matt 5:43) in the sense of going to physical battle against them, but the new testament instructs Christians to the contrary; instead we are to love our enemies (Matt 5:44ff) under all scenarios.
Since the new testament condemns the American style slavery of African-Americans, passages like I Peter 2:18 must be talking about indentured servants. Our politically correct society would disallow indentured servitude today, but such a system would be much preferred to legalizing stealing through the current day practice known as bankruptcy (Romans 13:8a, Psalms 37:21a).
What American slave traders did was nothing short of kidnapping at gunpoint, and therefore sinful. And those that bought such slaves became a partaker in the slave traders’ evil deeds (II John verses 10-11). The new testament law says no to slavery.