Pre-Civil War U.S. slavery was illegal and unconstitutional under the common law, Magna Carta, and the habeas corpus. People cannot be detained without criminal charges first being filed! This was BEFORE the Thirteenth Amendment. Slaves filed many lawsuits to be freed. They won! So the South banned teaching slaves to read and write, so then they wouldn't know their rights. Abolitionists such as William Goodell and others wrote about these cases and the Constitution's many anti-slavery clauses. A resource guide with links to more, is at http://medicolegal.tripod.com/slaveryillegal.htm. The fact of slavery being always illegal and unconstitutional in the U.S. is not just dry history. It has implications for modern issues such as affirmative action and reparations.