Before slavery as it existed in America, slaves had the benefit of personhood. Jews “enslaved” by Egyptians were protected by certain laws and were still considered human. They were allowed families, were not bred as cattle, and were not sold away from their families.
“Enslaved” whites did not live their lives that way. They were indentured servants and the servatude lasted for a defined time, not a lifetime. Again, by law they still retained certain human rights and were afforded legal protections. They were not born into slavery, nor were their children or spouse made slave by virtue of their servitude.
People of Judeo-christian belief were charged to remember their slaves humanity and treat them humanely according to the Bible. It was only in American slavery, that Africans were declared inhuman by the church and the most evil form of slavery was born. Even those who are victims of modern human trafficking are still considered human.
This is the major difference that makes American Black slavery unique and the major reason it cannot and should not ever be compared to any other time in history. Ever.