Alma 43:11

yea, and they also knew the extreme hatred of the Lamanites towards their brethren, which were the people of Anti-Nephi-Lehi; which 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.

The Nephites also knew that the Lamanites hated the people of Anti-Nephi-Lehi. These people were called the people of Ammon. They would not fight. They had made a promise not to fight and would not break it. So if the Lamanites caught them, they would be killed.

They also knew the Lamanites hated the people of Anti-Nephi-Lehi—now called the people of Ammon. These people had made a covenant never to take up weapons again, and they wouldn’t break it. If they fell into Lamanite hands, they’d be slaughtered.