Because plantation owners were mainly in the southern states. Also because there were many people that bought them from the south than anywhere else :)
Its The Spanish-American War of 1898
The prosecution entered indictments against 24 major war criminals and seven organizations – the leadership of the Nazi party, the Reich Cabinet, the Schutzstaffel (SS), Sicherheitsdienst (SD), the Gestapo, the Sturmabteilung (SA) and the "General Staff and High Command", comprising several categories of senior military officers.[avalon 1] These organizations were to be declared "criminal" if found guilty.
I believe it is the 1st one but may be the 2nd one.