Alma 43:11

Yea, and they also knew the extreme hatred of the Lamanites towards their brethren, ^a who were the people ^b of Anti-Nephi-Lehi, who were called the people of Ammon—and they would not take up arms, yea, they had entered into a covenant and they would not break it—therefore, if they should fall into the hands of the Lamanites they would be destroyed.