The danger of the combination of the Zoramites and the Lamanites to the southeastern part of Nephite lands was so clear that the people of Ammon were moved to the land of Melek. That seems like a simple and effective solution, but it assumes that modern readers understand the more ancient agricultural societies. By leaving the land, the Ammonites left their crops. While they certainly harvested what they could, and would certainly begin farming again as soon as possible, the movement to a new land meant that they had to start over and that there was less land available on which to grow food.
The combination of the move and the need to start farming from scratch would immediately diminish some of the food available to support the army in what would become a protracted war.
Mormon tells his readers that he is going to give more attention to this war when he declares that “an account shall be given of their wars hereafter.” He also knows that he has accounts of Alma’s blessings to his sons that he wants to include in his record, and he will place those in the record prior to returning to the war in Alma 43:3.