Geographic: In order to “[come] up upon the north of the land of Shilom,” the Lamanites had to travel around Shilom and therefore attack on the south of Lehi-Nephi. This manuever would split the Zeniffite armies, but it also presumes that an attack on Lehi-Nephi would also defeat the fighting effectiveness of Shilom, or else any army from Shilom would approach the Lamanite southern flank with the army from Lehi-Nephi on the north. That would create a two-front battle and increase the difficulty for the Lamanites.
It would appear that they intended a rapid advance into Lehi-Nephi that would capture the city. With the capture of the city and the king, Mesoamerican rules of warfare would dictate the war ended. Only a plan that supposed such a rapid capture of Lehi-Nephi could justify the Lamanite army’s action of placing itself between to armies.
Anthropological: In addition to the armaments, we have two pieces of information about the way in which the Shemlon-Lamanites went to war. The second is that they wore a “leathern girdle.” In modern connotation, leather would be shoe leather, or perhaps a softer leather, but certainly without the hair of the hide. In Mesoamerican war dress, however, the clothing worn around the waist was the treated skin of an animal, frequently depicted in paintings as a jaguar skin. It is possible that the word “leathern” here is translating this general concept, and that the Shemlon-Lamanites wore typical Mesoamerican battle dress rather than our conception of leather.
The first additional information is unique. The Lamanites “had their heads shaved that they were naked”. It is important to note that the “naked” describes their heads, not the rest of their bodies (which had the “leathern girdle”). Mesoamerican war dress does not typically show clean shaven heads on the warriors. In fact, not only do the warriors have hair, they typically have some type of head covering, ranging from a helmet-like hat that mimics (or was) the head of an animal to a large headdress.
The shaved heads do not have a clear analog in Mesoamerican warfare, but there are two possibilities. The first is that this happens long enough before our visual recording of warriors as to be a different style. This is fully possible, as the depictions do come much later in time than this Book of Mormon event. The second possibility comes from the visual depiction of capture of a warrior by grabbing the hair on the top of the head. For instance, a Maya vase shows Lord Kan Xib Ahaw capturing warriors. There are three captors and three captured warriors. Each of the captured warriors is held by the hair in the left hand of the captor (Reents-Budet, Dorie. Painting the Maya Universe: Royal Ceramics of the Classic Period. Duke University Press, 1994, pp. 258-9). If this posture signals the defeat of the warrior and his capture, the absence of hair would indicate a determination not to be captured. It could be a visual signal of the determination and goal of the attacking force. Rather than a raiding party to gain tribute, this might be a party bent on blood-feud vengeance, a scenario supported by the known facts behind this particular conflict.