This group of people does not leave their land to go to the Nephites, but rather they “yield up” land to the Nephites. The meaning of this is unclear. There is no indication in any part of the text Mormon has given us that there was any mass movement of Nephites southward into the land of Nephi. Nevertheless, we have the clear indication that land is yielded up to the Nephites.
Perhaps the problem is created by Mormon being less that clear as to which lands are yielded up. The text states that it was “lands of their possession.” This is not “lands of their inheritance” so it probably does not mean the land of Nephi. It would be very unusual for the Lamanites to yield up the land of Nephi since it has been under exclusive Lamanite control for about two hundred years. What is more logical is that there is a withdrawal of Lamanite political influence from the land of Zarahemla. The Lamanites would have relinquished their most recent acquisition. This would explain how it is that we will find Nephi back in Zarahemla without any other indication of how Zarahemla returns to Nephite control. This passage must indicate the voluntary withdrawal of the Lamanites from their most recently conquered territories.
Textual: There is no chapter break at this point in the 1830 edition. In fact, this artificial division masks the outcome of this mass conversion of the Lamanites. As we return to the narrative in chapter 6, Mormon will be emphasizing the comparative righteousness of the Lamanites and Nephites, which is a direct outgrowth of this miraculous event described in this chapter.