The voice of Mormon is throughout these chapters and I see that he makes assumptions of what is motivating the people. I can't help thinking that he views this story about Captain Moroni through his experiences with being the leader of the Nephites in his own day. His people lack the faith to trust in God and he marvels at the power granted to Moroni's followers to overcome their enemies.
Alma 49:27 "Yea, he was exceedingly wroth, and he did curse God, and also Moroni, swearing with an oath that he would drink his blood; and this because Moroni had kept the commandments of God in preparing for the safety of his people. And it came to pass, that on the other hand, the people of Nephi did thank the Lord their God, because of his matchless power in delivering them from the hands of their enemies."
Mormon has the ability to see both the past and the future. Here he is testifying to us, his readers, about the connection between prosperity and keeping the commandments as he sees prophecy fullfilled in this time of the Nephites.
Alma 50:19 "And thus we see how merciful and just are all the dealings of the Lord, to the fulfilling of all his words unto the children of men; yea, we can behold that his words are verified, even at this time, which he spake unto Lehi, saying: Blessed art thou and thy children; and they shall be blessed, inasmuch as they shall keep my commandments they shall prosper in the land. But remember, inasmuch as they will not keep my commandments they shall be cut off from the presence of the Lord."
Unfortunately, the Nephites, as a whole, did not continue to keep the commandments. There arose contentions among God's people.
Alma 51:9 "But behold, this was a critical time for such contentions to be among the people of Nephi;"
Alma 53:9 "And thus because of iniquity amongst themselves, yea, because of dissensions and intrigue among themselves they were placed in the most dangerous circumstances."
The Lamanites, with help from dissenting Nephites, became bold enough to attack the cities. This called for more resources and the people of Ammon felt they should arm themselves and help in the defense of their brethren.
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."
To preserve the covenant their fathers made to never again raise their swords against another, the sons of Ammon unite to go with Helaman and fight. These young lads are protected as sign from God that He keeps his side of the covenants we make with him. One thing I have learned from the Book of Mormon is that keeping covenants is everything to God. We are helpless, in many ways, in this mortal life to control our fate, but we do have power to stay true to our covenants. Through the atonement of Jesus Christ we receive enabling power to live with adversities, and that power increases through keeping our covenants.