Under the Banner of Heaven by Jon Krakauer, 2003, Excerpts
It had become clear to Brigham that there was no future for the Saints anywhere near Hancock County. On September 24 he sent a letter to Governor Ford’s blue ribbon committee saying that in return for a cease-fire from the Gentiles, the Mormons would promise to vacate not only Illinois but the whole of the United States.
For the Saints’ next homeland, Brigham Young wanted to find a place that was both a long way from civilization and would seem repugnant to Gentile settlers, so that his people might live free from persecution. The overwhelming majority loaded up whatever possessions would fit into their wagons, abandoned the rest to their enemies, and followed Brigham into the wilderness. By May of that year more than six thousand Saints were plodding westward through the axle-deep mud, drawn by the promise of Zion.
The thirteen-hundred-mile emigration from Nauvoo was a grueling trial. On the journey west they were plagued with frostbite, diphtheria, scurvy, starvation, stillborn babies, tick fever, hostile Gentiles, and an epidemic of whooping cough that killed dozens of young children. More than six hundred Saints perished during that first grim winter.