As early as the publication of the Book of Mormon in 1830, LDS doctrine maintained that polygamy was allowable so long as it was commanded by God. The Book of Jacob condemned polygamy as adultery, but left open the proviso that "For if I will, saith the Lord of Hosts, raise up seed unto me, I will command my people; otherwise, they shall hearken unto these things."[41] Thus, the LDS Church today teaches that plural marriage can only be practiced when specifically authorized by God. According to this view, the 1890 Manifesto and/or 1904 Manifesto rescinded God's prior authorization given to Joseph Smith.
http://en.wikipedia.org/wiki/Mormonism_and_polygamy
My question is why God would have commanded polygamy in the short period of 1844 to 1890 (especially if there were more men than women among the pioneer Saints)?
How would this "raise up seed" to Him?