During the United States' westward colonization in the 19th century, one of the most cohesive groups to take advantage of the overland trails was the Mormons (Church of Jesus Christ of the Latter-Day Saints), on account of persecution and violence back east. While some did go all the way to California, most overlanding Mormons settled in Utah. Pitching out in Utah Territory ought to have been a refuge/semi-independent existence for the Mormons, but then the 1849+ gold rush happened. And Utah became a necessary transit point for the flood of emigrants to California. Well, transit point and conflict zone.
Because while some emigrants found that Mormons were good to trade with, attitudes often soured very quickly in both directions. Lacking roads, wagon trains and cattle herds rumbled through whatever fields and towns stood in their way, often tearing up the seasons' crops. Mormons who remembered themselves or their ancestors being assaulted and having their property destroyed back in the Midwest, in return, saw their chance to harass emigrants under the excuse that surely they had come from Missouri, Illinois, etc. It's important to remember we are talking about settled, established colonies/territories here. When violent (to people or property) incidents happened, parties went to court--and smashed right into a harshly divided Utah administration split between local, often ecclesiastically-appointed Mormon officials and federal administrators dispatched from Washington.
Basically, no one was happy. Emigrants felt they could not get justice from Mormon juries. Mormon officials believed federal delegates were overriding their sovereignty and territory rights. U.S.-sent officials complained that the LDS Church could and did essentially override their own decisions.
And in the 1850s, this concept of popular sovereignty had a peculiar importance in American politics that you might be more familiar with under the phrase "states' rights"--that is, it needed to serve as a code word, in the politics of President James Buchanan's Democratic party, for the defense of slavery. Mormon theological opinions--namely, polygamy--couldn't be allowed to tarnish the image of a seen-as-necessary principle.
With the complaints from Good Protestant Overlanders and fleeing federal officials combined with darkening attitudes towards Mormons and Mormonism as politically damaging, Buchanan by fiat declared a new (non-Brigham Young) governor of Utah and sent a cadre of troops as combination police officers/bodyguards in 1857. Young and the Mormon leadership either did not get this memo or had reasonable experience on which to believe this memo was a purposeful deception: they saw the incoming troops as an invasion force meant to impose martial law and renew persecution of Mormons. So they called up their own militia, prepared for doomsday scenarios, and forbid Mormon residents from dealing with or aiding non-Mormon overlanders.
As to why the Utah Expedition/Utah War is less often discussed, of course there are the general platitudes like "you can only study so much in one history class" "not enough people were killed to make it a significant war" "the U.S. soldiers were kind of wimpy and when the '57-58 winter was bad they kinda just gave up and went home." But to investigate more specifically to the historical context, I'd like to focus on one brutal event within the time frame of the Utah War: the Mountain Meadows Massacre.
Like other emigrant groups before them, the Baker-Fancher wagon train (named for its leader-organizers, John Baker and Alexander Fancher) out of Arkansas had counted on being able to wheel and deal with Mormon shopkeepers for supplies before they headed through mountains and desert. Not under the new apocalypse-coming statues of the LDS community, though. Frustrated, the Fancher party did two things. First, they stopped to camp at Mountain Meadows pass in southern Utah to rest and consolidate for the weary trip ahead in the face of fewer supplies than they had planned for. Second, they talked a massively violent rhetorical game against the Mormons. Not only were they going to give the Mormons trouble, not only were the incoming U.S. army troops going to give the Mormons even more trouble, but--the clincher--people in the Fancher party "knew people" who had oppressed the Mormons right out of Missouri, or maybe--some bragged--maybe they had been those people.
Local militia leaders Isaac Haight and John Lee were not about to let this slide. They determined to attack the wagon train while they were camped. They were evil-crafty about it, too--they paid a group of Paiute Indians in cattle to participate in the initial attack in September 1857.
But Lee in particular wasn't satisfied with a few deaths in a skirmish. With the terrified Fanchers huddled down where they could defend themselves but not actually escape (and the threat of winter--and not being able to pass the mountains--looming), he went in to negotiate their surrender. Children and the wounded would leave first, in wagons; women and older children next; finally the men would walk out.
But Lee didn't mean "surrender," he meant "lambs to the slaughter." The Mormon soldiers massacred the entire wagon train. Only a handful of very young children were allowed to survive (they were kidnapped/adopted by Mormon families).
Historians have called this the worst event in Mormon history, which you might expect from historians. But the Mormons knew it at the time, too. Heck, they knew it in advance, which is why Lee and Haight worked so hard to get the Paiutes to participate in the initial attack. And while white Mormons were responsible for the brutal massacre, Paiute participation gave them the opening to claim Indian responsibility for "yet another" wagon train attack. (As John Unruh demonstrated so categorically, the actual "Indian threat" to overlanders was borderline nil, and our stereotypes today are the result of pop culture tropes and rumors already current in the 1840s).
The interesting thing, though, is that blaming the Paiutes didn't work quite as neatly as Haight and especially Lee might have hoped. So the Mormon leadership, desperate to avoid being implicated in triggering the slaughter, turned Mountain Meadows into a pinpoint-local event instead. They offered up Lee as the scapegoat--he was excommunicated in 1870 and executed in 1877. Well, America's gossip mill loves a good gory bad guy making a bad end, which quieted things on the "back east" and government ends. And it's not like the Utah government was raring to make "the worst event in Mormon history" a topic of major discussion.
Nicely illustrative of how the Massacre slid out of historical memory is the fate of its physical commemoration through memorials and historic markers. In 1859, with the massacre still a fresh memory and knowledge of white domination of its perpetration bleedingly fresh, U.S. military officials (!) set up a massive monument at Mountain Meadows. Brigham Young himself apparently oversaw its destruction just months later. The U.S. rebuilt it; the Mormons destroyed it again.
In 1932, with Utah now a nice state and the LDS Church itself not directly involved in government in the same way as the territory days, the state historic commission determined to build a marker. Except...they basically hid it behind rocks several miles from the road, so no one would actually see it. To make things even worse: Juanita Brooks' 1950 book The Mountain Meadows Massacre, the first scholarly investigation of the event which laid much of the blame at the feet of Young and the LDS hierarchy, triggered two reactions. First, quietly, the LDS church undid Lee's excommunication very posthumously, recognizing that the extent to which he had been scapegoated was wrong. Second, also quietly, the church bought the land where the 1932 marker was--and razed it.
And as James Loewen discovered in his investigations for Lies Across America, as late as 1990, the "new, improved" marker firmly in U.S. government control still stated:
The Mountain Meadows Massacre is not a feel-good story on anyone's part. The emigrants--who are undeniably teh victims here!--have been built up in collective memory to look not so good (victim blaming is always the easy way out), the Mormons don't look good, the U.S. government doesn't even look all that good for giving the impression of invading a territory (bad PR, overwrought officials fleeing and stoking rumours/hatred in Washington, giving up after one blizzard). The massacre didn't fit pre-Unruh theories about horrible violent Indians; but the real story of Indian participation in the beginning plus being blamed for the later events doesn't particularly suit any political agendas in more recent decades. The Utah Expedition roots that helped spark the slaughter are a diversion from the "popular sovereignty is about slavery" narrative that drives what you might call the major plot line of U.S. political history leading up to the Civil War.
Historical memory is not inevitable: people control what does and doesn't get told, as well as how it gets told. With so much history out there, far more than anyone could ever hope to know--yes, agendas are going to drive what does and does get "told" and "remembered". And as the history of the Mountain Meadows Massacre's commemoration shows, in this case people on all sides had a much more vested interest in forgetting than remembering.
Mormon History! This is one of my favorite guilty pleasures! I'm going to assume that you are not Mormon, but if you are, please forgive me for explaining something you already know. If you look at current LDS sources for information about the early history of the LDS church you will find that it is all correlated. This basically means that the Church has simplified and whitewashed its history into something more socially acceptable. Because of this it can be difficult for active members of the Church to find sources and information that they consider acceptable. This is also why sometimes Mormons (or non-Mormons) will hear about something in Mormon history and feel like they should have known about it, but didn't. The Utah War in general, and Mountain Meadows Massacre in specific are good examples.
The Utah War is a period where Brigham Young was using his influence to try to control many aspects of the Utah Territory. Keep in mind that when the Utah War started the Mormon Pioneers (Saints) had been in the Salt Lake Valley for about a decade, and Brigham Young had amassed a huge amount of power in that time. This all started with the Mormon Reformation which is a time when Brigham Young started pushing the Saints to follow the law of polygamy, and accept him as the leader of the Church, Territory, and Army (Nauvoo Legion). You can learn a lot about this time period by reading Wife No. 19 by Ann Eliza Young. She also discusses how Young had become a dictator in Utah Territory at that time, and how his desires were turned into action and violence within Utah.
So, what actually happened? The simple answer is "not much" but, as with much of history, things are more complicated than they might at first look. As I recall the trouble started when the Willie-Martin Handcart Companies struck disaster in Wyoming in October 1856. In response to this tragedy the United States sent soldiers and investigators to Utah to try to figure out why such a disaster happened. While this might seem like a normal response, for Young it was an attack on him, his leadership, and his people. You can get an idea of how often he felt this way about any criticism by also reading the Journal of Discourses.
Young started to order the Saints to make the lives of Gentile soldiers (non-Mormons) difficult by doing things like spooking livestock, burning supply wagons, and harassing them. The Saints felt justified in doing this because of the persecution they had suffered in the past, and they wanted to stand up for themselves now. At this point things might have all blown over, if not for the death of Parley P. Pratt.
Pratt was murdered in Arkansas, while on a mission, by the jealous husband of a woman he had converted to Mormonism and wanted to take as a plural wife. Her husband found out, found Pratt and killed him. Sadly, at about the same time as Pratt's death a Pioneer company also from Arkansas set out for California. The Baker-Fancher party had nothing to do with the death of Pratt, but that was not the message the Saints received. By the time Baker-Fancher arrived in SLC there were many who believed that they were responsible for the death of a beloved Elder in the Church. The Saints refused to sells provisions to the group (or perhaps they were ordered not to), and the group moved south to Utah Valley and Provo where they were, again, unable to resupply. Finally they were told of a place further south where they could camp and try to regroup and figure out what to do to get across Death Valley and to California.
The Baker-Fancher party arrived in Mountain Meadows in early September 1857. They were the besieged by a group consisting mostly of Mormons dressed as Paiute Indians, although there may have been a few Paiute involved. After 3 days they were then massacred on September 11, 1857. Over 130 men, women, and children were killed, and only 18 children under the age of 8 were saved. Those children were raised for about a year by Mormon foster parents, some of whom had participated in the massacre, until they were rescued and returned to their families in Arkansas.
This was pretty much the end of the Utah War. The massacre stirred up too much attention, and with the polygamy also being pushed at the time there was pressure to back off and lie low for a while.
Sources I used (although much of this is from memory, so if I'm wrong I'll be happy to admit it):
Wife No. 19 by Ann Eliza Young was originally published in 1875 and is a somewhat contemporary telling of the same events.
The Journal of Discourses is a great source of information, but is very dense. I have not read all of them, and mostly only excerpts.
Massacre at Mountain Meadows is specifically about the event, and is also a good read.
The Year of Polygamy podcast is an amazing resource for all things polygamy, and early Mormon history related. Each episode is sourced on the website, and Lindsey Hansen Park has done an amazing job with it! Specific episodes about this subject are: episode 116: Frontier Massacres. I was at the recording of this episode, and it was fantastic. Episode 43 is about violence in the 1850's in Utah, and episode 44 is specifically about the Utah War.
Special thanks to /u/mythrin for all his amazing knowledge, and for giving me the courage to be a normal person who talks about Mormon history. (Also, if you show up because I summoned you, can you let me know if there is anything I need to add?)
This is my first post on Ask Historians. I will be available for follow up questions/comments for most of the day today and tomorrow.