I can help with that, actually. ^^ Xehanort betrayed Ansem the Wise because he believed that there might be a better understanding if they explored the dark areas of the heart. Ansem, who had experienced the powers of the darkness and knew the trouble it had caused, denied his apprentice's request to study further. Xehanort disobeyed him, and worked with who we now know as Zexion, Lexaeus, Xigbar, and Xaldin to look past the light in one's heart. The darkness consumed them and soon they became heartless as well, thus creating the Nobodies we know.


Now, on another topic...well, sort of. What I've heard is that Vexen was working on cloning and such before he was destroyed. The rumor is that he made clones of all the Organization members, and that it was only clones we had to fight in KH2. How would this fit a new storyline? Heartless follow the keyblade, and naturally so do Nobodies, as they strive to unleash Kingdom Hearts and renew their real selves. The only way they can do this is with the help of the Keyblade bearer...and though Sora is no longer our main character, there will be a new one to come along...