In Alma 27:28 we learn of the people of Ammon, who were recently converted Lamanites, with a vow that “they never could be prevailed upon to take up arms.” However, we find later in the Book of Alma (53:13-14) they do this very thing, and it is Helaman who has to insist that they keep their promise.
see also Vogel, Joseph Smith: The Making of a Prophet (Salt Lake City, UT: Signature Books, 30 April 2004), 232.
“And they did look upon shedding the blood of their brethren with the greatest abhorrence; and they never could be prevailed upon to take up arms against their brethren; and they never did look upon death with any degree of terror, for their hope and views of Christ and the resurrection; therefore, death was swallowed up to them by the victory of Christ over it.”
Alma 27:28 – The Book of Mormon (Salt Lake City, UT: The Church of Jesus Christ of Latter-day Saints, September 2008 Edition), 277.
“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. 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.”
Alma 53:13-14 – The Book of Mormon (Salt Lake City, UT: The Church of Jesus Christ of Latter-day Saints, September 2008 Edition), 343.