 He was imprisoned, along with his brother Hyrum Smith, at Carthage Jail, where they were attacked by a mob and murdered.After a succession crisis, most of the Mormons united under Brigham Young, who organized an evacuation from Nauvoo and from the United States itself after the federal government refused to protect the Mormons.Young and an eventual 50,000–70,000 would cross the Great Plains to settle in the Salt Lake Valley and the surrounding area.