We have here the beginning of a new conflict, as those who have not converted to the gospel begin mobilising against those who have, which includes the royal family. Thus in verses 1 & 2:
And it came to pass that the Amalekites and the Amulonites and the Lamanites who were in the land of Amulon, and also in the land of Helam, and who were in the land of Jerusalem, and in fine, in all the land round about, who had not been converted and had not taken upon them the name of Anti-Nephi-Lehi, were stirred up by the Amalekites and by the Amulonites to anger against their brethren.
And their hatred became exceedingly sore against them, even insomuch that they began to rebel against their king, insomuch that they would not that he should be their king; therefore, they took up arms against the people of Anti-Nephi-Lehi.
The old king confers the throne upon his son (not King Lamoni), whom he gives the new snappy name of Anti-Nephi-Lehi (I guess he really liked it) and dies, leaving Anti-Nephi-Lehi, Lamoni, Ammon and his brothers and others to confer about what is to be done.
What happens next is a particularly memorable episode. The new converts are very grateful for the gospel and the mercy they have felt from God:
Now, these are the words which he said unto the people concerning the matter: I thank my God, my beloved people, that our great God has in goodness sent these our brethren, the Nephites, unto us to preach unto us, and to convince us of the traditions of our wicked fathers.
And behold, I thank my great God that he has given us a portion of his Spirit to soften our hearts, that we have opened a correspondence with these brethren, the Nephites.
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.
However, they are concerned that by attempting to defend themselves, they could once more veer into sin. They thus decide on a different plan:
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.
Oh, how merciful is our God! And now behold, since it has been as much as we could do to get our stains taken away from us, and our swords are made bright, let us hide them away that they may be kept bright, as a testimony to our God at the last day, or at the day that we shall be brought to stand before him to be judged, that we have not stained our swords in the blood of our brethren since he imparted his word unto us and has made us clean thereby.
And now, my brethren, if our brethren seek to destroy us, behold, we will hide away our swords, yea, even we will bury them deep in the earth, that they may be kept bright, as a testimony that we have never used them, at the last day; and if our brethren destroy us, behold, we shall go to our God and shall be saved.
And now it came to pass that when the king had made an end of these sayings, and all the people were assembled together, they took their swords, and all the weapons which were used for the shedding of man’s blood, and they did bury them up deep in the earth.
And this they did, it being in their view a testimony to God, and also to men, that they never would use weapons again for the shedding of man’s blood; and this they did, vouching and covenanting with God, that rather than shed the blood of their brethren they would give up their own lives; and rather than take away from a brother they would give unto him; and rather than spend their days in idleness they would labor abundantly with their hands.
Thus in a striking act of symbolism, the Anti-Nephi-Lehies bury their weapons in the ground so they can no more be “stained”, and reinforce that symbolic act with a covenant to never use weapons again. This is what motivates their decision to “not even make any preparations for war; yea, and also their king commanded them that they should not”.
Some have read this account – and what follows, in which many are killed by their persecutors “prais[ing] God even in the very act of perishing under the sword” (v. 23), act act that causes at least some of their persecutors to forebear and to even join them, “relying on the mercies of those whose arms were raised to slay them” (vv. 24-25) – as an example of pacifism and even an endorsement of it. This seems to me to be less likely. Considered as a whole, it is clear that while the Book of Mormon is very concerned with the subject of what might be termed “just war” – including legitimate reasons to fight, and what constitutes moral conduct within it – it does depict occasions when it is right to fight, and examples of those who engage in warfare without compromising moral standards. To me, what seems more clear is that the Anti-Nephi-Lehies are very concerned about the specific acts for which they have felt guilt and have repented of, and are anxious not to tread a path that could lead back to sin. This feels like it could be more widely applicable, not just to killing people. If we have repented or are repenting of some specific sins, there may be situations we may wish to avoid, not because those situations are in themselves sin, but because they could so easily lead us back into specific former sins.
For more of a discussion on the pacifism (or not) of the Anti-Nephi-Lehies and implications on what the Book of Mormon teaches about the morality of warfare, Duane Boyce has written an article on the subject that is very worth reading: “The Ammonites were not Pacifists”
At the end of this chapter, we learn that some of the primary movers of the persecution were the Amalekites and Amulonites, only one of whom (one Amalekite, Alma 23:14; another episode we have no details of but which could be interesting) had converted before the persecutions, and none of whom do so in remorse at the killings. Mormon draws out a general point:
And thus we can plainly discern, that after a people have been once enlightened by the Spirit of God, and have had great knowledge of things pertaining to righteousness, and then have fallen away into sin and transgression, they become more hardened, and thus their state becomes worse than though they had never known these things.
Repentance was possible for them – one apparently does do so – but while it is possible, their previous choices mean that it is much harder for them to choose that option. It is perhaps a scary notion, but while we have agency, we do not make our decisions in a vacuum, and our spirits and our natures are not unaffected by the previous decisions we make. If we keep choosing wrong and rejecting truth, that has spiritual consequences on our ability to choose right and discern truth in the future.