God allows certain kinds of slavery in his Law. Slavery isn't inherently sinful. The problem is in how it is conducted. No human can own another outright, but God can delegate authority temporarily. Your sensibilities are irrelevant.

If a conquered people remains enslaved to Israel for many generations, then Israel has failed in her mission to be a light to all nations. These slaves ought to be made into Israelites and then released in the seventh year.

#deuteronomy 20:11 #shoftim