Gadianton’s Robbers find no purchase among the Lamanites1
A plague from and for the Nephites
Helaman 6:37 And it came to pass that the Lamanites did hunt the band of robbers of Gadianton; and they did preach the word of God among the more wicked part of them, insomuch that this band of robbers was utterly destroyed from among the Lamanites.2
Preaching the word helped the Lamanites3 eliminate the Gadianton Robbers4 , 5. They took the cleansing of themselves from those robbers very seriously. Also, remember that “Lamanites” were never really a single nation like the Nephites were. The robbers may have had trouble finding much purchase among a more distributed society, or they might have fled to a different un-monitored place. In every case, the Gadianton Robbers were spawned and preyed particularly on the Nephite social structure.
Footnotes
1 Header image from https://ldsmag.com/is-the-book-of-mormons-depiction-of-guerrilla-warfare-realistic/
2 Scripture at https://www.churchofjesuschrist.org/study/scriptures/bofm/hel/6?lang=eng&id=p37#p37
3 “Lamanites,” though conceived in my childhood as an homogenous opposite to the Nephites, were actually a disparate grouping meaning just “not Nephites,” which included any number of indigenous peoples outside the discussion of the Book of Mormon.
4 A fascinating piece of apologetics remarking on the anachronistic-to-Smith depiction of guerilla warfare at https://ldsmag.com/is-the-book-of-mormons-depiction-of-guerrilla-warfare-realistic/
5 Were the Gadianton Robbers one of the first historical accounts of organized crime? Discussed in an article by Wu Mingren at the church-unaffiliated https://www.ancient-origins.net/history/gadianton-robbers-0011462