By 1857, tensions had again escalated between Mormons and other Americans, largely as a result of accusations involving polygamy and the theocratic rule of the Utah Territory by Brigham Young. In 1857, U.S. President James Buchanan sent an army to Utah, which Mormons interpreted as open aggression against them. Fearing a repeat of Missouri and Illinois, the Mormons prepared to defend themselves, determined to torch their own homes in the case that they were invaded. The relatively peaceful Utah War ensued from 1857 to 1858, in which the most notable instance of violence was the Mountain Meadows massacre, when leaders of a local Mormon militia ordered the killing of a civilian emigrant party that was traveling through Utah during the escalating tensions. In 1858, Young agreed to step down from his position as governor and was replaced by a non-Mormon, Alfred Cumming. Nevertheless, the LDS Church still wielded significant political power in the Utah Territory.