When you're starting to deal with the slave situation, there is an obvious tension between the natural law on the one hand, and the positive law on the other hand. According to Justinian, and virtually everybody else at the time, slavery was against the laws of nature, which was essentially thought to guarantee the freedom of every individual, but nonetheless, it was part of the positive law. The abolition of slavery in the United States was one of the issues that triggered the bloodiest conflict that this country had ever entered into. It was about trade, but essentially the issue that drove everybody, was the issue about slavery. The reason why it's so difficult, is if you come within the legalistic tradition there's a strong system of vested rights, if you come within the natural law system, none of this really counts for anything at all. It's just very difficult through the art of fine persuasion to work a compromise. Lincoln, of all people, understood this better than anybody else. If you read some of his statements and so forth, having to do with Dred Scott and so forth, he made concession after concession to the Southerners on these kinds of issues because he understood the enormity of trying to upset one of these kinds of arrangements. When you do modern American constitutional law, it's really important to understand the level of doubt, anxiety, and turmoil that took place between the period of Dred Scott, which was decided about 1856 or so, and the adoption of the 13th, 14th, and 15th Amendments. Two very different traditions have to come to peace. We know which one won in the end, but if you're trying to do history it's much better to understand the turmoil as it unfolded to the parties who were involved, rather than looking at the result that came out of it and treating it as though it's inevitable; and therefore, understanding not a whit about how it was that the debate was framed in the earlier period. Good historians are extremely careful about all of that stuff, and when you start to do so you can see just how perplexing an issue slavery turns out to be. This is not to say that it's part of the new program of a political party to re-institute the institution, nobody believes that of course, it's just a way to say that transitions are always messy, even if the moral position at the end of the day is crystal clear.