Mormon attributes their victory to Jehovah, in accordance with the covenant of the land. The Nephites were sufficiently righteous to warrant Jehovah’s protection, and they had received it. Mormon underlines that it was not only a fulfillment of the protection part of the covenant, but also that there was “exceedingly great prosperity in the church because of their heed and diligence which they gave unto the word of God.”
This ends the nineteenth year, and with the end of the nineteenth year, Mormon ended his chapter, which our modern editions have split into chapters 45–49. Even though a battle and a year have ended, the war has not ended, and will continue in the next chapter. In such situations, where there is no other reason for Mormon to create a chapter ending, he often breaks between years, allowing for a set of five years. Depending upon how he wants to tell his stories, sometimes the fifth year starts the next chapter, or sometimes it ends the current chapter. Nevertheless, there is a noticeable emphasis on five-year blocks of time. See the comments on Alma 1:1 for more information.