Mormon fundamentalism (also called fundamentalist Mormonism) is a belief in the validity of selected fundamental aspects of Mormonism as taught and practiced in the nineteenth century, particularly during the administration of Brigham Young, an early president of The Church of Jesus Christ of Latter-day Saints (LDS Church). Mormon fundamentalists seek to uphold tenets and practices no longer held by mainstream Mormons (members of the LDS Church). The principle most often associated with Mormon fundamentalism is plural marriage, a form of polygyny first taught by Joseph Smith, Jr., the founder of the Latter Day Saint movement. A second and closely associated principle is that of the United Order, a form of egalitarian communalism. Mormon fundamentalists believe that these and other principles were wrongly abandoned or changed by the mainline LDS Church in its efforts to become reconciled with mainstream American society.