1845 Mormons commit an act of "blood atonement"

Phineas Wilcox is stabbed to death by fellow Mormons in Nauvoo, Illinois, because he is believed to be a Christian spy. Wilcox was one of the first victims of "blood atonement," an old Mormon doctrine conceived of by Brigham Young that taught that murder is sometimes necessary in order to save a sinful soul.
The murder of Wilcox reflected the serious and often violent conflict between the Church of Jesus Christ of Latter-day Saints and the surrounding communities. Joseph Smith, who founded the Mormon Church in 1830, had been living with his followers in Missouri, where they had various conflicts with locals, including an armed skirmish with the state militia. In 1838, Governor Lilburn Boggs, who was wounded four years later by an unidentified sniper at his home, signed a military order directing that the Mormons be expelled or exterminated: "The Mormons must be treated as enemies and must be exterminated or driven from the state, if necessary, for the public good."
Smith and the Mormons fled across the Mississippi to Nauvoo, Illinois, which quickly became the second most populous town in the state. But there were conflicts and tensions in Nauvoo as well. When a local newspaper printed editorials claiming that the religious leader was a fraud, Smith sent a group of followers to destroy the newspaper office. He was then arrested and sent to jail, where a lynch mob tracked him down and killed him.
Brigham Young, who quickly took command of the church and its followers, tried to stifle any dissent and banish his rivals. The killing of Phineas Wilcox was part of his consolidation of power. Tensions with other communities continued to escalate, and, a year later, over 2,000 armed anti-Mormons marched on Nauvoo. Young decided that it no longer was wise to stay in the area. He led his flock west and settled in the Salt Lake Valley, where he and his followers would become instrumental in founding the state of Utah.