Utah War, in U.S. history, conflict between Mormons and the U.S. government. In the spring of 1857, President James Buchanan appointed a non-Mormon, Alfred Cumming, as governor of the Utah Territory, replacing Brigham Young, and dispatched troops to enforce the order. The Mormons prepared to defend themselves and their property; Young declared martial law and issued an order on Sept. 15, 1857, forbidding the entry of U.S. troops into Utah. The order was disregarded, and throughout the winter sporadic raids were conducted by the Mormon militia against the encamped U.S. army. Buchanan dispatched (Apr., 1858) representatives to work out a settlement, and on June 26, the army entered Salt Lake City, Cumming was installed as governor, and peace was restored.
See L. R. and A. W. Hafen, ed., The Utah Expedition, 1857–58 (1958); N. F. Furniss, The Mormon Conflict, 1850–1859 (1960).