It’s interesting to me that teaching the gospel is what destroys this Nephite version of the mafia, called the Gadianton robbers, rather than a get-even-with-’em attitude of returning violence for violence. Destroy seems like an odd word to use, since in this case, what actually happened was that many people were saved. Then again, having people accept the salvation of Jesus Christ is the best way to destroy Satan’s efforts for ultimate evil. 

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.” 

https://www.lds.org/scriptures/bofm/hel/6?verse=37&lang=eng#p37