<P> The journey was taken by about 70,000 people beginning with advance parties sent out by church leaders in March 1846 after the 1844 assassination of the Mormon leader Joseph Smith made it clear the group could not remain in Nauvoo, Illinois--which the church had recently purchased, improved, renamed, and developed because of the Missouri Mormon War, setting off the Illinois Mormon War . The well - organized wagon train migration began in earnest in April 1847, and the period (including the flight from Missouri in 1838 to Nauvoo), known as the Mormon Exodus is, by convention among social scientists, traditionally assumed to have ended with the completion of the First Transcontinental Railroad in 1869 . Not everyone could afford to transport a family by railroad, and the transcontinental railroad network only serviced limited main routes, so wagon train migrations to the far west continued sporadically until the 20th century . </P> <P> Since its founding in 1830, members of the LDS Church were often harshly treated by their neighbors, partially due to their religious beliefs, sometimes as a reaction against the actions and the words of the LDS Church and its members and leaders . These and other reasons caused the body of the Church to move from one place to another--to Ohio, Missouri, and then to Illinois, where church members built the city of Nauvoo . Sidney Rigdon was the First Counselor in the LDS First Presidency, and as its spokesman, Rigdon preached several controversial sermons in Missouri, including the Salt Sermon and the July 4th Oration . These speeches have sometimes been seen as contributing to the conflict known as the 1838 Mormon War in Missouri . As a result of the conflict, the Mormons were expelled from the state by Governor Boggs, and Rigdon and Smith were arrested and imprisoned in Liberty Jail . Rigdon was released on a writ of habeas corpus and made his way to Illinois, where he joined the main body of Mormon refugees in 1839 . In 1844 Joseph Smith, and his brother Hyrum Smith were killed by a mob while in custody in the city of Carthage, Illinois . In 1846, religious tensions reached their peak, and in 1848 mobs burned the Latter - day Saint temple in Nauvoo . </P> <P> According to church belief, God inspired Brigham Young, Joseph Smith's successor as President of the Church, to call for the Saints (as church members call themselves) to organize and head West, beyond the western frontier of the United States (into what was then Mexico, though the U.S. Army had already captured New Mexico and California in late 1846). During the winter of 1846 - 47, Latter - day Saint leaders in Winter Quarters and Iowa laid plans for the migration of the large number of Saints, their equipment, and their livestock . It was here that Brigham Young first met Thomas L. Kane, a non-Mormon from Philadelphia with deep personal connections to the Polk administration . Kane obtained permission for the Mormons to winter on Indian territory, and the site was originally called Kanesville . Brigham Young continued to trust Kane throughout his own lifetime, particularly as an intermediary with the often hostile Federal government . This major undertaking was a significant test of leadership capability and the existing administrative network of the recently restructured Church . For his role in the migration, Brigham Young is sometimes referred to as the "American Moses ." </P> <P> Brigham Young personally reviewed all available information on the Salt Lake Valley and the Great Basin, consulting with mountain men and trappers who traveled through Winter Quarters, and meeting with Father Pierre - Jean De Smet, a Jesuit missionary familiar with the Great Basin . The wary Young insisted the Mormons should settle in a location no one else wanted, and felt the Salt Lake Valley met that requirement but would provide the Saints with many advantages as well . </P>

Who took over the mormon leadership and began the westward trek