When the Mormons first came to Utah in 1847 it still belonged to Mexico. A year later, at the end of the Mexican War, it became a territory of the United States, not gaining statehood until 1896. During the Utah War (1857-1858), President James Buchanan sent troops to Utah, along with a new governor. In that "war" there was only one skirmish where gunfire was exchanged, and the only casualties were two horses -- so the news of killings on both sides was only rumor.

See Historical Background for more details.