I would not want the thread to become a discussion of slavery, but I do want to say that there are many kinds of slavery, and were many kinds in the past. For example, the Greeks had slaves. You might consider indentured servents slave or child laborers, slaves. The slavery practiced in the young United States was particularly efficient and cruel, though. The fact that just being of darker skin made it possible for you to be distinguished as a slave meant that it was much harder to escape, both physically, and to escape people's attitude toward you, once you had been emancipated.
American slaves were treated more like livestock; their children were born into slavery, there was no set period to work one's way into freedom , such as indentured servents, they had no rights to really own land, their spouses and children could be removed from them at any time. They could be legally killed by their owners, for a whim.
Because they were believed to be intriniscically inferior, it was felt the were "meant" for slavery, as opposed to an indentured servent, or a warrior who had been captured and forced into slavery. These persons were slaves only due to their circumstances and once freed, they recovered their original position in society.
All slavery is not the same, but American Slavery was perhaps the most hopeless and destructive of them all, with the longest lasting consequences.
This thread seems to stay alive because there is a strong interest or at least strong feelings about race. As long as the discussion is not attacking, rude, or truly racist then I would think it can continue to live.