New Canaanites

Unlike many other pre-war religions, groups of Mormons still survive in the wasteland, mostly in the area that used to be known as the state of Utah. Though truly brutal groups like Caesar's Legion will not hesitate to enslave or kill Mormons, most tribals and other organizations leave the Mormons alone, knowing that they often will voluntarily give medical or other aid to groups who need it. The people tolerate the Mormons’ preaching because finding help with relatively benign conditions is rare. One of the most notable Mormon settlements is New Canaan.

Mormons extermination
Disclaimer: it is episode present at cancelled New Canaan design document, so it isn't van Buren canon. Because of some Mormons reluctancy to help other people it is contrary with J.E. Sawyer's Fallout Role-Playing Game also.
 * 2220-2233 period: New Jerusalem intolerant authorities policy was no commerce with outsiders from other, failed communities, refugees or tribals,
 * in 2233 year a number of angry tribals, raiders and disassociated attackers gang up on New Jerusalem and sack it, kiling most of the Mormons in the process (even more then 90% of population),
 * in 2248 year almost half of residents of New Canaan (about fifty people) leave to New Jerusalem led by bishop Mordecai; New Jeruslaem was city founded in 2190 year by Vault 70 residents in the ruins of Salt Lake City,
 * in 2250 year bishop Mordecai and five others return to New Canaan as sole survivors ot their attempt resettle New Jerusalem.

It is not certain, who wasted New Jerusalem resettlers in 2250 year. On the one hand, if tribals and other organizations leave the Mormons alone, it should Caesar's Legion. On the other hand it could be Hounds of Hecate or Blackfoot tribals, powder gangs or other raiders, like in examples of 215 powder gang attacking New Canaan or thre tribal attacks on Burham Springs.