Chronological: [in that same year]: Mormon does not name a year, but assumes that we understand that “in that same year” refers to the last noted event:
Mormon 1:18
18 And these Gadianton robbers, who were among the Lamanites, did infest the land, insomuch that the inhabitants thereof began to hide up their treasures in the earth; and they became slippery, because the Lord had cursed the land, that they could not hold them, nor retain them again.
Mormon 1:19
19 And it came to pass that there were sorceries, and witchcrafts, and magics; and the power of the evil one was wrought upon all the face of the land, even unto the fulfilling of all the words of Abinadi, and also Samuel the Lamanite.
This creates an interesting contrast between the war in which Mormon will now be engaged and the previous. It is possible that there is a distinction in the composition of the enemy, with the previous combatants being Lamanites, and only now a combination of Lamanites and Gadianton robbers. This fits into our hypothesis that the Gadianton robbers were Teotihuacán military castes that had merged into various Lamanite peoples and influenced them to differing religion and increased militarism.
Social: Mormon implies much, and tells us little. The essential information is that he becomes the leader of the armies of the Nephites at a young age. What he does not tell us is perhaps some of the more important socio-cultural information we could have for the Nephites in the post-Messianic-visit era. Since he does not tell us, we must try to fill in the blanks.
The first thing that we learn from Mormon’s statement is that there is a single leader for a single army. When we combine this piece of information with the understanding that there are Nephites in Bountiful and Zarahemla as two named lands, and presumably a larger territory, this tells us that there has been re-established a Nephite political unit that has a unified leadership to which the various cities look for defense. This leads us to suspect that the Nephites had reestablished the reign of judges, as it is unlikely that they would have allowed kings given their antipathy to kings and the social meanings that were imported with the Mesoamerican kingship conceptions.
The second probable understanding is that there were men trained in the military rather than simply conscripted from their farming duties. Were this not so, there would be no reason to look to a young man as a general. With a decentralized and non-professional military, each unit would have had a leader, and the symbolic overall leader would go to respect and age, not to a young man. The only reason for selecting a young man is skill, and that skill would not only come from a professional military training, but a system sufficiently formalized that the members of that profession were recognized. Only with a professional and recognized training for military men would a man of Mormon’s age be within the scope of vision of those selecting a leader for the army.
Knowing that Mormon was in a military training, and that he had learned to read and write, further supports the hypothesis presented that both he and his father had been part of the court retainers of the Nephite political leader, and that the leader must have been Ammaron. Assuming that the Nephites were following Mesoamerican social structures, those who were in the courts, but not in the line of inheritance, were those most likely to be scribes. Their prominent social position would also place them in a position of visibility and social worthiness to be a leader of an army. The only facet remaining is the particular reason for selecting Mormon, and that would be a demonstrated skill that was respected by those making the choice of the leader of the armies.