Well, I took your advice and did a google search on the subject. The closest thing I found to the 'Laws of War' was a Yale website with a collection of treaties and conventions grouped under the title "Laws of War". The problem is that all but one or two post-date the Civil War, and I don't see how one could accuse the Union or the confederacy of breaking laws that weren't even adopted until after the fact.
the first internationally accepted LoW document (that i know of!) was a papal bull signed by Julius II, which set out the rules for the protection,humane treatment,medical treatment & repatriation of POWs. all the many european states followed the dictates of the papal bull, even those countries like GB, which were not all roman catholic.
Julius II was the warrior pope that was the mentor of Michaelangelo.
for dixie,sw