In the agrarian democracy Americans were building, both land and votes mattered. Non-Mormons felt threatened by the Mormons' practices of settling in concentrated numbers and voting as a bloc. The Missouri Mormons were forced to relocate twice in the mid-1830s. In Ohio, an anti-Mormon mob tarred and feathered Smith in 1832, and he left the state in 1838 after civil lawsuits and a charge of bank fraud followed the failure of a bank he had founded. By the time he arrived in Missouri that January, non-Mormons were assaulting Mormons and raiding their settlements; a secret Mormon group called the Sons of Dan, or Danites, responded in kind. That August, Missouri Governor Lilburn Boggs issued an order to his state militia directing that the Mormons "be exterminated or driven from the State for the public peace." Two months later, 17 Mormons were killed in a vigilante action at a settlement called Haun's Mill.
The Mormons moved next to Illinois, founding the town of Nauvoo there in 1840 under a charter that gave the city council (which Smith controlled) authority over local courts and militia. This settlement grew to about 15,000 people, making it the biggest population center in the state. But in 1844, authorities jailed Smith in the town of Carthage after he destroyed a Nauvoo newspaper that had alleged he was mismanaging the town and had more than one wife. At that point, Smith's polygamy was acknowledged only to the LDS Church's senior leaders. In a raid on the jail, an anti-Mormon mob shot the church founder to death. He was 38.
"Few episodes in American religious history parallel the barbarism of the anti-Mormon persecutions," historian Fawn Brodie wrote in her 1945 biography of Smith. At the same time, she added, the early Mormons' relationships with outsiders were characterized by "self-righteousness" and an "unwillingness to mingle with the world." To non-Mormons in Illinois, Brodie wrote, "the Nauvoo theocracy was a malignant tyranny that was spreading as swiftly and dangerously as a Mississippi flood." Amid continuing harassment in Illinois, the Mormons prepared to leave.
After Smith's death, the LDS Church's ruling council, the Quorum of the Twelve Apostles, took control of church affairs. The lead apostle, Brigham Young, a carpenter from Vermont and an early convert to Mormonism, eventually succeeded Smith. In February 1846, he led the beginnings of an exodus of some 12,000 Mormons from Illinois, determined to establish their faith beyond the reach of American laws and resentment. Brigham Young biographer Leonard J. Arrington has written that Young and other church leaders knew about the Great Salt Lake Valley from trappers' journals, explorers' reports and interviews with travelers familiar with the region.
At the time, most of what would become the American Southwest belonged to Mexico, but Young believed that that nation's hold on its northern frontier was so tenuous that the Mormons could settle there free from interference. In the spring of 1847, he led an advance party of 147 from an encampment in Nebraska to the Great Salt Lake Valley, arriving that July. Over the next two decades, some 70,000 Mormons would follow; the grueling journey would be one of the defining experiences of the LDS Church.
In February 1848, Mexico sealed its defeat in the Mexican-American War by signing the Treaty of Guadalupe Hidalgo, ceding to the United States what is now California, Nevada, Utah, Texas and parts of Arizona, New Mexico, Colorado and Wyoming. Just six months after arriving in their new Zion, the Mormons found themselves back under the authority of the United States.
To preserve self-rule, church leaders quickly sought official status, petitioning Congress in 1849 first for territorial status, then for statehood. The land they sought was vast, running from the Rockies to the Sierra Nevada and from the new border with Mexico all the way to present-day Oregon. Congress, guided in part by the struggle between forces opposing and condoning slavery, designated a Utah Territory, but not before reducing the area to present-day Utah, Nevada, western Colorado and southwestern Wyoming.
Territorial status gave the federal government greater authority over Utah affairs than statehood would have. But President Millard Fillmore inadvertently set the stage for a clash with his choice for the new territory's chief executive. In 1850, acting partly in response to lobbying from a lawyer named Thomas L. Kane, a non-Mormon who had advised Mormon leaders in previous ordeals, Fillmore named Brigham Young governor of the new Utah Territory.
Young ran the Utah Territory much as Smith had run Nauvoo, and conflicts between religious and secular authorities soon re-emerged. The Mormon leaders were suspicious of both the character and intent of federal appointees, such as a judge who was found to have abandoned his wife and children in Illinois and brought a prostitute to Utah. And over the next seven years, a succession of federal officers—judges, Indian agents, surveyors—came to the territory only to find that the governor would circumvent or reverse their decisions.
Young "has been so much in the habit of exercising his will which is supreme here, that no one will dare oppose anything he may say or do," Indian agent Jacob Holeman wrote to his superior in Washington, D.C. in 1851—in effect going over Young's head (Young was also the territory's superintendent of Indian affairs). Surveyor General David Burr reported that Young told him federal surveyors "shall not be suffered to trespass" on Mormon lands. Through the mid-1850s, federal appointees returned East frustrated or intimidated or both, and some of them wrote books or articles about their travails. Anti-Mormon sentiment spread, inflamed particularly by reports of polygamy.