The 1838 Mormon War, also known as the Missouri Mormon War, was a series of armed conflicts between Mormons (Latter Day Saints) and other settlers in northern Missouri during the summer and fall of 1838. Initially characterized by mutual vigilante violence, it escalated into direct intervention by the Missouri state militia. The conflict concluded with the issuance of the Missouri Executive Order 44, which mandated the extermination or the expulsion of the Mormons from the state.
Early Latter Day Saints settled in Missouri driven by religious revelations instructing them to "gather" in Kirtland, Ohio, and Jackson County, Missouri. Facing increasing hostility from neighboring settlers, an 1833 crisis resulted in their forceful eviction from Jackson County by vigilantes. The Missouri legislature created Caldwell County in 1836 as a "compromise" for displaced Mormon settlers; however, the relocation of Mormon leaders from Kirtland in early 1838 intensified fears of Mormon consolidation and expansion in the state.