The Utah War (1857–1858), also known as the Utah Expedition, Utah Campaign, Buchanan's Blunder, the Mormon War, or the Mormon Rebellion, is an armed confrontation between Mormon settlers in the Utah Territory and the armed forces of the United States government.

The confrontation lasts from May 1857 to July 1858. There are some casualties, mostly non-Mormon civilians.

The war has no notable military battles.