In 1838, Missouri Witnessed the Missouri Mormon War

Not strictly speaking a war, but the first of three small-scale armed conflicts between Mormon settlers and their non-Mormon neighbors. The third, the Utah War, finally established that territory, and then state, as a permanent home for the faithful. The second, based on its mentions in Wikipedia, seems to be called the lesser-known Illinois Mormon War, which followed the death of Joseph Smith, the religion's founder, in 1844. But the Missouri conflict was also pivotal to the religion's history, as a key part of its move ever-westward after its founding in upstate New York.