User blog comment:Vivaporius/AT Idea: Imperial Civil War/@comment-3341288-20120409204527/@comment-3398633-20120409231924

Lion, angry about Caliban's destruction, and...perhaps believes his father's polices lead to the downfall of the Imperium, as he didn't see what happened at the end of the Heresy. Gulliman perhaps does some soul searching, and figures that he could do a better job by himself without he's father's shadow stopping him from going through with his plans for peace. Remember, Ultramar is by far the most peaceful and productive part of the Imperium, an accomplishment done by Gulliman, not the Emperor. Pride maybe?