On October 27, 1838, Missouri governor Lilburn Boggs issued the Extermination Order, which ordered all Mormons to leave the state or be exterminated. From the article:
"MISSOURI STATE ARCHIVES
The Missouri Mormon War
In the 1830s, “Mormonism” commanded center stage in Missouri politics. Joseph Smith and the church he founded in New York State in 1830 quickly gained converts, attracting considerable attention throughout the northeastern United States. Originally named the Church of Christ, it subsequently became the Church of Jesus Christ of Latter-day Saints. Believers were referred to as “Mormons” because of the church’s adherence to “The Book of Mormon,” their companion scripture to the Bible wherein the story of Jesus appearing to the ancestors of the Native Americans was told.
That same year, Smith dispatched a handful of missionaries to Missouri’s western border to preach the “restored gospel” to the Native American tribes concentrated there. In 1831 Smith proclaimed that God had designated western Missouri as the place where “Zion” would be “gathered” in anticipation of Christ’s second coming. His small band of missionaries soon became a steady stream of converts anxious to establish Zion in Missouri.
Within a few years, the migration and settlement of Latter-day Saints in frontier Missouri led to events that would earn Mormonism a painful place in Missouri history. The state’s “Old Settlers” (usually recent immigrants to the Missouri frontier themselves) characterized the Mormon settlers as fanatics whose clannish behavior made a mockery of republican institutions by placing power in the hands of a single man. The Mormons claimed that they had done nothing wrong, and were attacked for their religious beliefs. Violence broke out in 1833 as the “Old Settlers” under the guise of “extra-legal” justice took the law into their own hands.
It soon became clear that Missouri non-Mormons and Mormons could not live in the same area harmoniously. In 1836 a “separate but equal” proposal was finally devised to solve this problem, whereby the state legislature created a new county, “Caldwell,” in northwest Missouri as a sort of Mormon “Indian Reservation.” But the booming Mormon population, swelled by the immigration of thousands of eastern converts doomed this to failure, as Mormon settlers burst the borders of Caldwell County and spilled into neighboring counties. Violence broke out again at an election riot in 1838. Old Settler mobs and Mormon paramilitary units roamed the countryside. When the Mormons attacked a duly authorized militia under the belief it was an anti-Mormon mob, Missouri’s governor, Lilburn Boggs, ordered the Saints expelled from the state, or “exterminated,” if necessary. The conflict’s viciousness escalated, however, even without official sanction, when, on October 30, 1838, an organized mob launched a surprise attack on the small Mormon community of Haun’s Mill, massacring eighteen unsuspecting men and boys. Over the next year, around eight thousand church members, often ragged and deprived of their property, left Missouri for Illinois.
The Missouri State Archives’ “Mormon War Papers” shed light on this frequently misunderstood episode of Missouri history. This collection includes documents such as Governor Bogg’s infamous “Extermination Order”, but also many lesser known, and less appreciated, documents that are well worthy of study, such as the report of the legislative joint committee appointed to investigate the “disturbances” between Mormons and non-Mormons. Included also are such items as legislative debates and the governors’ state of the state addresses in which the “Mormon problem” is discussed. The collection also includes the criminal hearing of Joseph Smith and other church leaders for treason and other crimes."