Amalickiah places Zoramites in important positions. They were a people most recently part of the Nephite lands, and therefore would have had the best and most recent information about Nephite strengths and weaknesses. Of course, one of the weaknesses would be in the southeastern section where the Zoramites had once been central to the defense of Nephite lands from that entry point.
Having done so, the army moves. At this point, Mormon halts his story of the Lamanite actions and returns to a focus on Chief Captain Moroni. To do so, Mormon moves back slightly in time to show what Moroni had been doing during the time that Amalickiah had been consolidating power among the Lamanites.