This verse is the fulfillment of the vow made by the Nephites in Mormon 3:10. Mormon has removed himself from leadership of the army because he knows that they are fighting without the Lord, and engaging in what Mormon understands will be a futile offensive. Rather than fight defensively, as Mormon had been doing, these Mormon-less Nephites take the attack to their Lamanite/Gadianton enemies. The result is that they are defeated, and when they retreat, they are in a sufficiently weakened state that they lose the city of Desolation. The descriptions of the results of war have shifted in these last wars from the previous wars. We have noted that the previous wars tended not to be for territorial acquisition, but for the imposition of tribute, retaining the local leadership. Now the wars are shifting to a more virulent type, and one of the accompanying figures is the taking of “many prisoners.”
The shift in the nature of the warfare is likely the result of the influence of the Gadianton robbers in the Lamanite army, and the connection made in this commentary between the Gadianton robbers and the Teotihuacan influence. Part of this influence would extend to an escalation in the cult of war, and the taking of prisoners would be an indication of the intention of using those prisoners in human sacrifice.