Moroni uses the captured Lamanites as slave labor. They not only bury the dead, but build the fortifications for the city Bountiful. Mormon notes the use of the forced labor, and feels some need to explain it. The Nephite armies are split into a two front war, and they are fewer than the Lamanites to begin with. Moroni’s forces are already spread thin, and those who would have been able to labor on the construction process are already in the army and deployed for a more active defense. The Lamanites provide a ready work force that is now available for the defensive construction, and as Mormon indicates, it was easier to guard them with a few men than it would have been to have that many of Moroni’s men perform the labor.
The result of the labor is that the city of Bountiful becomes a very strong city. Mormon notes that it “became an exceeding stronghold ever after.” This would appear to suggest that Bountiful continued as a fortified Nephite city up to Mormon’s day.
Translation: We have another case of an inserted correction in the text. As always, there are the two possibilities for the author of the insertion, Mormon or Joseph. This one appears to suggest Mormon as the author of the insertion because the logic of the insertion requires that the writer hold both the concept of the land of Bountiful and the city of Bountiful in their head, with clear distinctions in the meaning of the two. There would appear to have been some preference for a reference to the land of Bountiful, as that is the first writing, but then the correction is entered for the city. This insertion is required because anyone who clearly understands the difference between the land and city would understand the impossibility of creating the described defenses for the land of Bountiful, hence the rapid change to the city.
It is less likely that Joseph would have been as understanding of the land/city difference. Certainly there are many modern readers of the text who have passed those terms and not comprehended the considerable difference between the two. This perceptual difference would have been much more likely to have been present with Mormon, suggesting that this instance should be seen as his correction to a word written in error.