What best describes the history of Mormonism in the US?

Mormonism is the predominant religious tradition of the Latter Day Saint Movement. It was founded by Joseph Smith in Western new York in the 1820s. It distinguished itself from traditional Protestantism. A prophet leader Joseph Smith was killed in 1844. After that most Mormons followed Brigham Young on his westward journey to the Utah Territory.

Mormon fundamentalism maintained practices and doctrines such as poligamy (plural marriage), or the United Order, form of egalitarian communalism. In the 1890 Manifesto the president of the Church of Jesus Christ of Latter Day Saints announced the official end of plural marriage. This was the reason why several groups of Mormons broke with this church forming several denominations of Mormon fundamentalism.

Some sources have claimed that there are about 6.5 million Mormons in the United States today.