This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Having already been driven out of Ohio and then out of Jackson County, Missouri, the Latter-day Saints resettled in Caldwell and Daviess counties, Missouri, where escalating tension with their neighbors grew into what is remembered as the Missouri Mormon War. Fighting reached its peak at the Battle of Crooked River in October 1838, and two days later, on 27 October, Governor Lilburn Boggs answered it with Executive Order 44, directing that the Mormons must be treated as enemies and must be exterminated or driven from the state, language that stayed formally on the books, unrescinded, until 1976. State militia carried the order out, and three days after it was issued a mob massacred seventeen Latter-day Saints, including children, at Haun's Mill.
Thousands fled that winter into neighboring Illinois, where they built the city of Nauvoo into a substantial refuge, but the persecution followed them across the state line. Joseph Smith and his brother Hyrum were murdered by a mob at the Carthage jail in June 1844, and renewed mob violence, including a September 1846 siege by roughly eight hundred armed men, forced the remaining Saints out of Nauvoo entirely, most of them crossing out of the city across that winter and the following spring.
What this changed for the Latter-day Saints' spread was the collapse of any hope that the church could gather permanently inside the settled eastern United States under a state government's protection. An extermination order, a militia that carried it out, and two mob killings within eight years persuaded the church's leadership that survival meant moving the whole body of believers somewhere no state government could reach, the same conclusion that sent Brigham Young west within a year of Nauvoo's fall.