Geographic: The land Bountiful is the land immediately to the south of the narrow pass. By fortifying the land of Bountiful, Teancum would be protecting the narrow pass as well. Moroni’s intent in this is telling. He does not want the Lamanites to be able to “have power to harass them on every side.” The possession of the narrow path by the Lamanites would cut off a retreat area. The Lamanites are already in a very strong position, but not yet to the point where they could “harass… on every side.”