Wilford Woodruff is elected the fourth resident of The Church of Jesus Christ of Latter-day Saints. An early convert to Mormonism, he becomes president when he's 82 and on the run from the law because he's wanted for violating anti-polygamy laws.
Mormons and their church are laboring under a great deal of pressure from the United States government because of their polygamy and there is the very real threat of the church being destroyed entirely. For leading politicians and clergy in America, polygamy is on par with slavery as a moral evil and the latter had recently been destroyed by war. They weren't going to allow polygamy to continue, whatever the cost.
It will thus be up to Wilford Woodruff to make the difficult decision of ending Mormon polygamy in order to save Mormonism. In fact, right after his election as president of the Mormon church, he refuses to give permission for plural marriages to take place, so he's already moving in the direction of eliminating polygamy.