Alma 34:11 - 34:15
Alma 43: 11 Yea, and they also knew the extreme hatred of the Lamanites towards their brethren, who were the people 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.
Not only did the Nephites know of the hatred of the Lamanites towards them but also their extreme hatred they had towards the Anti-Nephi-Lehi’s or the Ammonites. Ammonites were the Lamanites who covenanted never takes up arms even if attached by their enemies. They would suffer death rather than defend themselves.
Alma 43: 12 And the Nephites would not suffer that they should be destroyed; therefore they gave them lands for their inheritance.
The Nephites were so taken with the Ammonites covenant, that they had given them property that they could use to support themselves.
Alma 43: 13 And the people of Ammon did give unto the Nephites a large portion of their substance to support their armies; and thus the Nephites were compelled, alone, to withstand against the Lamanites, who were a compound of Laman and Lemuel, and the sons of Ishmael, and all those who had dissented from the Nephites, who were Amalekites and Zoramites, and the descendants of the priests of Noah.
Not only did the Nephites give land to the Ammonites, but they said they would defend these people if they would support the troops stationed to protect them. The Ammonites agreed and a large portion of their increase was used to support their guardians and their families. So it was up to the Nephites to defend on their own the Ammonites against all the Lamanite armies which consisted of the descendents of Laman, Lemuel, the sons of Ishmael and all those who were once Nephites and were now Lamanites such as the Amalekites, Zoramites and the descendent of the priest of Noah.
Alma 43: 14 Now those descendants were as numerous, nearly, as were the Nephites; and thus the Nephites were obliged to contend with their brethren, even unto bloodshed.
Now the descendants of the decenters were almost as numerous as the Nephites themselves. So it was now the obligation of the Nephites to defend themselves against their own relatives who had gone over to the Lamanites.
Alma 43: 15 And it came to pass as the armies of the Lamanites had gathered together in the land of Antionum, behold, the armies of the Nephites were prepared to meet them in the land of Jershon.
The armies of the Lamanites had gathered in the land of Antionum. The armies of the Nephites were gathered in the land of Jershon to met them.