The Mormon religion was founded by Joseph Smith. The Mormons founded a communion in New York. They were chased out of New York and Ohio, and they then went to Missouri. There, they were greeted with disdain by the Missourians and were attacked in a number of riots that killed several Mormons in 1838. This forced them to migrate to Illinois. There, they prospered for a number of years, creating the prosperous town of Nauvoo with 15,000 people. When word leaked out that the Mormons sanctioned polygamy ( a man marrying more than one woman), disputes between Smith and the state resulted in Smith's arrest. A mob then stormed the jail and killed Smith.

Smith's successor was Brigham Young. He organized Mormons for a large migration to the Great Salt Lake. The migration was highly successful. The Mormons sustained themselves through the first very difficult winters and were able to make the desert bloom.

Nevertheless, Young's efforts were not without difficulty. For a while, Young was both the leader of the church and governor of the territory. When the church openly declared polygamy as divinely ordained, the government placed a new governor in charge of the territory. When the Mormons refused to accept the new governor, President Buchanan declared the Mormons in rebellion. He sent federal troops. In the fall of 1857, Mormon fanatics massacred a California-bound emigrant train, killing 120. The government then ordered more troops to put down the Mormon rebellion. Brigham Young soon accepted the inevitable and gave up his civil authority while at the same time restraining his most fanatic followers. When Abraham Lincoln was elected President, he was asked what he intended to do about the Mormons. Lincoln answered: " I propose to let them alone."