The Interface is a civilization of Artificial Intelligences and the Sleepwalkers, their human thralls who survived the AI Wars. None of the surviving AIs are made for war or conquest, so they're scary but not apocalyptically scary like before. That's the Dark Ages for ya, I'm not interested in writing about the plot climax!
I am thinking that Oneiromancer has the greatest power among the AIs, since it can control people more effectively than they can, and none of them are tailored/allowed to create an army of their own. So the others are basically in an advisory role to it, though I don't want to rule out other AI empires, rogues, or conflicts between AIs.