The second half of 4 Nephi traces the gradual reappearance of division after generations of unity, beginning with the reemergence of pride tied to wealth and fine clothing, then a formal split back into groups again calling themselves Nephites and Lamanites, and finally the return of the Gadianton robbers, the secret combination whose earlier rise had been narrated at length in Helaman. By the book's final verses, the text describes widespread wickedness once more, setting up the sustained final wars that the following book, Mormon, will narrate in full.
Because so much time and so little detail are compressed together, 4 Nephi has drawn attention less for any single episode than for the shape of its arc: a society reset to something close to an ideal after Christ's visit, sustained for generations, and then eroded gradually rather than destroyed suddenly, which later Latter-day Saint teaching often reads as a caution about complacency following genuine spiritual renewal.
4 Nephi never explains why unity eventually gives way; the text simply notes pride creeping back in through a portion of the people who begin wearing costly apparel again, which later commentary within the tradition has read as a deliberately understated account of how prosperity itself can erode the conditions that produced it.