The Thirteenth Amendment is about as straightforward as any of the first ten amendments (I find it interesting to notice that the most obvious and natural amendments tend to be the shortest).
Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.
While there is nothing that I would dare add to that amendment and I doubt that anyone needs a lesson in the context behind its adoption I do wonder how our nation might be different if the issue of slavery had been resolved by the process of adopting this amendment rather than fighting a war before then adopting this amendment.
I would not suggest that the issue would have been “resolved” by 1865 even to the degree that it was with the Civil War, but I would not be surprised if the outcome would have been to more completely lay to rest the prejudices that were so openly accepted 100 years later and which we still feel among our society today. (No, electing a black president does not prove that we have no racism or bigotry remaining in our society – in case there was anyone who entertains such a notion.)