The people of Anti-Nephi-Lehi are an enigma. At first, they were Lamanites and sworn enemies of the Nephites and as Lamanites would have been engaged in the raiding, capturing, enslavement and slaughter of Nephites.
However, the sons of a Nephite king, newly endowed with evangelical zeal, end up converting entire Lamanite cities to the Nephite faith, such that the converted Lamanites make a covenant to adopt their religion and become extreme pacifists, burying their weapons and preferring to be slaughtered by the sword than to defend themselves violently.
After these newly converted Lamanites uproot and are taken in as refugees, by their former enemies, they offer up their adolescent sons to fight in a Nephite war, rather than breaking their pacifistic covenant(Alma 24; Alma 53), which theoretically disqualifies them as pacifists. Why did the adults practice extreme pacifism in their own lives but also aggreed to have their teenaged sons go to war, on their behalf?
Reading this episode of Mormon's book, through a mesoamerican lens, may shed light on these eccentricities. One major clue as to why can be found in the words of their king:
And behold, I also thank my God, that by opening this correspondence we have been convinced of our sins, and of the many murders which we have committed. And I also thank my God, yea, my great God, that he hath granted unto us that we might repent of these things, and also that he hath forgiven us of those our many sins and murders which we have committed, and taken away the guilt from our hearts, through the merits of his Son.
And now behold, my brethren, since it has been all that we could do, (as we were the most lost of all mankind) to repent of all our sins and the many murders which we have committed, and to get God to take them away from our hearts, for it was all we could do to repent sufficiently before God that he would take away our stain— Now, my best beloved brethren, since God hath taken away our stains, and our swords have become bright, then let us stain our swords no more with the blood of our brethren.
Behold, I say unto you, Nay, let us retain our swords that they be not stained with the blood of our brethren; for perhaps, if we should stain our swords again they can no more be washed bright through the blood of the Son of our great God, which shall be shed for the atonement of our sins.
The people of Anti-Nephi-Lehi saw themselves as murderers, the whole people. The reason they all buried their weapons is because they all saw themselves as guilty of murder, as a group; and that part of their repentance, in accepting the Nephite religion, recquired the abandonement of warfare, even if the Nephites themselves still fought wars.
However, there is a moral difference, both in the Bible and Book of Mormon, between killing people in war and murder. However, these newly converted Lamanires didn't see it that way and there is a reason why.
The Mesoamerican Cult of War
In Mesoamerica, religion and warfare were symbiotic; one of the functions of war was to procure human victims, so that they might be sacrificed to the gods. In the words of Michael Coe, when reffering to the far latter practice of the Aztecs, the victims of human sacrifice "were ideally enemy warriors. ... It is incontrovertible that some of these victims ended up by being eaten ritually"(1). Given the conservative continuity of mesoamerican culture, this practice might also have existed in the pre-classic.
If the people of Anti-Nephi-Lehi were as steeped in mesoamerican religion as other mesoamericans were then leaving that faith would recquire leaving all of it, including warfare. There adolescent sons however, weren't seen as being old enough to be guilty of murder, because they presumably weren't old enough to be guilty of participating in the older faith, assuming they even did participate at all.
(1)Michael Coe; Mexico: From the Olmecs to the Aztecs (Seventh Edition)pg 197-198.