Why did Mormons practice polygamy?

In the early 1830s, Joseph Smith received a revelation that the Lord wanted Smith to renew the practice of polygamy. Although uncomfortable with the idea, many people recorded that Smith was commanded by an angel to initiate this practice. The records of this angel appearing to Joseph Smith come from some of Smith’s plural wives like Helen Mar Kimball, Eliza R. Snow, Mary Rollins Lightner, and Zina Huntington. Other accounts of Smith’s angelic visitation come from Benjamin F. Johnson, Joseph Lee Robinson, Lorenzo Snow, Erastus Snow, and Orson Pratt. In these accounts, the angel visited Smith multiple times and on the final visit (probably a third visit), Smith was threatened with eternal destruction if he did not follow God’s command to implement the practice of Joseph Smith polygamy.

In the mid-1830s, Smith probably married his first plural wife: Fanny Alger. Alger and her family joined the church and she lived with the Smith family in 1833. The marriage did not last and Alger moved away from Ohio with her family. She married another man, Solomon Custer. When Alger was asked about her relationship with Joseph Smith she replied, “That is all a matter of my own.”

After several years, Smith began introducing his revelation about polygamy to a few church members in Nauvoo. Plural marriage sealings began among this small group of trusted church leaders in Nauvoo. By the time Smith was murdered in 1844, Joseph Smith’s wives numbered approximately 30-40 women.