Mormon doesn’t tell us too much about this particular army, other than it is another Lamanite army. That leaves a lot of unanswered questions. Is this a coordinated effort from a single Lamanite commander, or is this a second army from a completely different Lamanite political unit? We simply don’t have enough information to tell us, though it is a question that is of historical interest. The arguments for the two possibilities are as follows:
There is not enough evidence to choose between these alternatives.
Textual: We no return to the events. This particular event is rather spectacular because it suggests that this particular invasion of Zarahemla was rather massive, with two different armies appearing within days. Had Mormon written his text during the heated events being described, this second appearance would have received a much greater emphasis than it does here. Rather than Mormon’s explanation of the cursing of the Amlicites and Lamanites, we would have had a greater discourse on the tremendous military pressures being placed on a people who had to meet such large armies so quickly in succession.
We don’t get that for two reasons. The first is that Mormon is not writing at that time and so can distance himself from the events. The second is that it really is not Mormon’s purpose to describe wars. Rather, Mormon is detailing the events that are leading to the coming of Christ. At this point we are only 87 years from the birth of Christ, and Mormon still has a lot of explaining to do to get from the relatively righteous Nephites to those who are persecuting the believers just before Christ’s birth. These events are part of an explanation of the spiritual war, not the physical one. For that reason we get the spiritual aside of the cursing of the Lamanites and the Amlicites. It is those spiritual witnesses of these wars that are most important to Mormon.