Chronology: Mormon does not name a year, but “in that same year” obviously refers to the last noted event, which was the slippery earth, the presence of Gadianton robbers, and the fulfillment of Abinadi’s and Samuel’s prophecies (Morm. 1:18–19).
The specification of Lamanites and Gadianton robbers as combatants suggests that only Lamanites had been involved in the first war, in which Mormon’s father may have been killed. If the Gadiantons were, in fact, new combatants, it would fit my hypothesis that they were Teotihuacan military castes that had merged with various native (“Lamanite”) groups, influencing them toward more militarism and toward a new religion. (See Helaman, Part 1: Context, Chapter 3, “The Gadianton Robbers in Mormon’s Theological History: Their Structural Role and Plausible Identification.”)
Culture: Mormon omits virtually all socio-cultural information about the Nephites in this era; but it is possible to tentatively fill in some blanks.
The fact that Mormon is appointed “the leader [singular] of their armies [plural]” when Nephites live in both Bountiful and Zarahemla (at least) tells us that the Nephites have a unified polity, whose cities look to it for defense. Given the two models of judges or monarchies, rule by judges seems the more likely. When the Nephites were reconstituted as a political entity (implied, not directly mentioned) it is most likely that they returned to the more recent model of the judges, a model that was associated with a venerated ruler, Mosiah2.
It also seems likely that the Nephites had a trained army. A decentralized and unprofessional army would have had local leaders for each unit; the highest leader would have been a respected and older man of high status, not a young man. The only reason for selecting a young man is skill. Such skill must have come from formal and professional training whose practitioners were publicly recognized.
If Mormon has military training and is literate, it is further support for my hypothesis that both he and his father had been courtiers to Ammaron, the ousted Nephite political leader. Assuming that the Nephites were following Mesoamerican social structures, those who were courtiers but not in the line of succession were most likely to be scribes. Their social prominence would also make them candidates to lead an army. Perhaps they were somewhat parallel to the Japanese samurai who were expected to demonstrate both their martial and artistic skills. Assuming that other candidates also filled this niche, then Mormon’s skill, respected by those choosing the general, would have been the decisive factor, though how they had occasion to recognize that skill is not known.