The latter part of the book of Alma is well known for its description of war and tactics. That long military narrative arc might lead a reader to assume that Mormon, as a military general, was very interested in war and, therefore, spent time in it. There must be a different explanation, for in these verses we learn that there was a terrible war in the fifteenth year of the reign of the judges (see verse 7). It was “a tremendous battle; yea, even such an one as never had been known among all the people in the land from the time Lehi left Jerusalem.” The greatest battle in Nephite history up to that point is described in just two verses.
Mormon includes no tactics, no descriptions of valor, and no stories of inspirational faithfulness. He simply says that “tens of thousands of the Lamanites were slain and scattered abroad,” and that “there was a tremendous slaughter among the people of Nephi.” That is the whole story of the most devastating battle in Nephite history up to that point.
While Mormon certainly was a general, and obviously admired Captain Moroni, Mormon’s interests in war had more to do with the people and their decisions than the battles themselves. This battle doesn’t involve personalities that interest him or move his purposes along, so he gives only the abbreviated indication of what happened.