In addition to people going north, there were some dissenters who went south. The Lamanites are in the south, and as has happened before, the dissenters incite the Lamanites to attack. Moroni’s son, Moronihah, leads the victorious Nephite army, and the Lamanites are beaten back. There are no tactics discussed, and other than simply saying that there was an attempt that was defeated, we know very little about this war, save that it occurred in the thirty-ninth year, and that Moronihah led the Nephite armies.
The “account of Alma, and Helaman, his son, and also Shiblon, who was his son” ends in the fortieth year. This is an appropriate time to end a record, particularly if Mormon is following Mesoamerican calendrics. Mesoamericans used a base-20 system, and in that system, twenty had the symbolic significance that ten would in a decimal system. In Maya, a twenty-year period was given a name: katun. Thus, the book ends in a very symbolic two-katun year.
This will be more important as we begin the book of Helaman, and as we note why the beginning of the book of Helaman perhaps was more properly the ending of the book of Alma, save for the desire to end on the symbolic forty-year count.