By the election year of 1844, Joseph Smith, the controversial founder of the Church of Jesus Christ of Latter-day Saints, had amassed a national following of some 25,000 believers. Nearly half of them lived in the city of Nauvoo, Illinois, where Smith was not only their religious leader but also the mayor and the commander-in-chief of a militia of some 2,500 men. In less than twenty years, Smith had helped transform the American religious landscape...