Did early Mormons marry and have sex with teen brides, like the FLDS today?
Yes. According to church history, Mormon Church founder Joseph Smith married eight underage girls, including one 14 year-old, two 16 year-olds and his own foster daughters. These marriages were not normal for the 1840s, especially to a man in his thirties that was already married. See: Teen polygamy in Early Mormonism.
