How did slavery in America differ from different from earlier forms of slavery?

Industrialized Slavery(which inc. American slavery) dehumanized people, it made them livestock traded by ship-load, and very disposable, if one died, you demanded another. 

Traditional/Ancient Slavery was actually a very regulated(in most cultures), form of working to clear a debt, often there was also a time-limit, after which you were clear of debt, and set free as a slave.