Only a few words and phrases are used by Mormon to describe the feelings and spiritual conditions of the Nephites before they entered into the Ten-Year peace treaty (AD 350–360) with the Lamanites and Gadianton robbers (Mormon 2:19–29). According to Mormon 2:28, in the year AD 350, the Nephites (led by Mormon) made a ten-year peace treaty with the Lamanites and even with the Gadianton robbers. They bought those ten years of peace at a very high price, by promising to give up the entire land south of the narrow neck of land.
As numbers often do, this date and these ten years probably mean something. The year 350 was the seventh occurrence of the fifty-year cycle—the seventh Jubilee year—from the birth of Jesus. They negotiated a ten-year treaty in accordance with Hebrew custom in observance of this special sabbatical-jubilee.
In Mormon 3:1 we learn that during that decade Mormon had made sure that his people were employed in preparing for the inevitable resumption of battle. Nevertheless, that decade was the only time in Mormon’s life that he had a peaceful period long enough to work on a major project, such as the Book of Mormon. Mormon was forty years old in AD 350, and he was sixty years old when the ten-year peace expired. It would appear that it was during this Jubilee decade that he had time and the opportunity to work on the abridgment.
At the same time, if he had married in about AD 331, his son Moroni could have been born a year or two later, and he would have been about 18 or 19 years old in AD 350—old enough to have been taught and trained by Mormon in the languages of his people and in the skills required to abridge records and to make and inscribe plates. When Mormon died in AD 385, Moroni knew exactly how to pick up where Mormon had left off. It makes sense that Moroni would have grown up as his father’s research and writing assistant.
Promptly after those ten years, in Mormon 3:4, the king of the Lamanites wrote a letter warning that they would resume hostilities. Apparently, this king was willing to live exactly by this ten-year treaty. It must have been a very solemn and somewhat religiously or symbolically oriented treaty for people on both sides to be willing to take a ten-year break from the war. The Lamanites were no doubt tired and probably needed a little rest too, but that would not have required a full decade in order to regroup. The bigger problem must have been within the Nephite camp. And, indeed, it was not more than two years after this ten-year time-out that Mormon would utterly refuse to lead the Nephites any longer because of their vengefulness and hatred.
Book of Mormon Central, “Why Is The 10-Year Peace Treaty Important? (Mormon 3:1),” KnoWhy 228 (November 10, 2016).