Alma 53:11 - 53:15
Alma 53: 11 And because of their oath they had been kept from taking up arms against their brethren; for they had taken an oath that they never would shed blood more; and according to their oath they would have perished; yea, they would have suffered themselves to have fallen into the hands of their brethren, had it not been for the pity and the exceeding love which Ammon and his brethren had had for them.
These Lamanites had sworn an oath never to take up arms again. They were now pacifists and would rather die at the hands of their enemies than to raise a sword in their defense. If it had not been for the grave concern by Ammon for their lives, they would have been slaughtered at the hands of their own people. But Ammon brought them out of the land of Nephi and they were taken in by the Nephites. They were given land so they could live in peace without the threat of death by the Lamanites.
Alma 53: 12 And for this cause they were brought down into the land of Zarahemla; and they ever had been protected by the Nephites.
Because of all these things, these pacifist Lamanites were brought settled near Zarahemla so they could be protected.
Alma 53: 13 But it came to pass that when they saw the danger, and the many afflictions and tribulations which the Nephites bore for them, they were moved with compassion and were desirous to take up arms in the defence of their country.
However, these people could see the great sacrifice the Nephites were making not only to protect themselves but sheltering these people as well. They could not help but be willing to give up their oath and join with the Nephites in their own defense.
Alma 53: 14 But behold, as they were about to take their weapons of war, they were overpowered by the persuasions of Helaman and his brethren, for they were about to break the oath which they had made.
As a result, these folks were going to take up arms again, but Helaman pleaded with them not to do so. They had made a sacred oath with the Lord and they needed to stick with it.
Alma 53: 15 And Helaman feared lest by so doing they should lose their souls; therefore all those who had entered into this covenant were compelled to behold their brethren wade through their afflictions, in their dangerous circumstances at this time.
And just like a person who had given up drinking and if they should take another drink they might return to drinking again, Helaman was afraid that if they got a taste of fighting and killing they might return to their previous ways and become a blood thirsty people once again. So these Lamanites living under the protection of the Nephites had to stand by and witness the sacrifice of men and material for their defense.