Without any advanced notice, the first three verses of this chapter come as a sudden shock to the reader. They tell us that Mormon the great historian and compiler of the Book of Mormon has turned his high calling over to his son, Moroni, to complete the record. We learn a lot more from these verses:
After the great battle at Cumorah, the Lamanites set out to fulfill their passionate zeal to slay every Nephite in the land who would not join them. Apparently some did join them. Others fled southward trying to escape.