I am glad/surprised to see that people aren't freaking out over "the slave thing". It makes the long boring task of explaining that the American (once a slave always a slave, racial slavery, hereditary slavery, etc) is only one type and depending on the technological advancement of a society slavery is a better alternative to starvation and/or execution. (Imprisonment of non-nobles is relatively recent given the scarcity of food and the preferred usage of labor for military or, well, said food issue.)
Oh, well I did the explanation anyway... (Think I will just link this post in the future...)