After continued difficulties and persecution in Illinois, Young left Nauvoo in 1846 and led his followers, the Mormon pioneers, to the Great Salt Lake Valley. The group branched out in an effort to pioneer a large state to be called Deseret, eventually establishing colonies from Canada to present-day Mexico. Young incorporated the LDS Church as a legal entity, and governed his followers as a theocratic leader, serving in both political and religious positions. He also publicized the previously secret practice of plural marriage, a form of polygamy. By 1857, tensions had again escalated between Latter-day Saints and other Americans, largely as a result of the teachings on polygamy and theocracy. The Utah Mormon War ensued from 1857 to 1858, which resulted in the relatively peaceful invasion of Utah by the United States Army, after which Young agreed to step down from power and be replaced by a non-Mormon territorial governor, Alfred Cumming. Nevertheless, the LDS Church still wielded significant political power in the Utah Territory as part of a shadow government. At Young's death in 1877, he was followed by other powerful members, who continued the practice of polygamy despite opposition by the United States Congress. After tensions with the U.S. government came to a head in 1890, the church officially abandoned the public practice of polygamy in the United States, and eventually stopped performing official polygamous marriages altogether after a Second Manifesto in 1904. Eventually, the church adopted a policy of excommunicating its members found practicing polygamy and today seeks to actively distance itself from "fundamentalist" groups still practicing polygamy.