Mormonism's distinctive view of marriage arises from its distinctive view of mankind itself:
"Central to LDS theology is the belief that men and women existed as spirit offspring of heavenly parents in a premortal life. . . . Latter-day Saints believe that the marital and family bond can continue in the post-earth life, and indeed is necessary for eternal life, or life in the Celestial Kingdom with God the Father; Mother in Heaven; Jesus Christ, and other glorified beings."Encyclopedia of Mormonism, Vol.2, MARRIAGE
The Mormon Prophet Joseph Smith instituted Celestial Marriage late in his careerwithin a year of his murder in Illinois. The practice of Celestial Marriage springing up within Mormonism doubtless fueled the flames of antagonism towards Mormonism by their "gentile" neighbors. Shortly after Joseph Smith was murdered in Carthage, Illinois, the Mormons themselves were driven out of the state and migrated to Utah. In Utah the Latter-day Saints, under the leadership of Prophet and President Brigham Young, continued the practice of Celestial Marriage. That practice nearly led to war with the United States.
Celestial Marriage is Required for
It is Polygamous in Nature.