 The largest group of Mormons (LDS Church) accepted Brigham Young as the new prophet/leader and emigrated to what became the Utah Territory.There, the church began the open practice of plural marriage, a form of polygyny which Smith had instituted in Nauvoo.Plural marriage became the faith's most sensational characteristic during the 19th century, but vigorous opposition by the United States Congress threatened the church's existence as a legal institution.