In the years before America’s bloody Civil War ended black slavery, it was euphemistically called the nation’s “peculiar institution.”

Historian Amy Tanner Thiriot says it was even more peculiar in the prewar Utah Territory, where Southern converts to Mormonism, making the journey to their faith’s desert refuge in the late 1840s and early 1850s, brought about 100 slaves with them.

“The slave owners [had] to adjust how they dealt with their slaves outside of the South,” Thiriot says. “They were used to controlling slaves by violence, slave patrols and the threat of sale.”

Thiriot — who will speak on “Black Mormon Pioneer Experiences” on Thursday at 7 p.m. at the LDS Church History Museum, 45 N. West Temple, in downtown Salt Lake City — says these Southerners found little support for their slaveholding ways in Zion.

“They found themselves,” she explains, “surrounded by largely Northern and European [Mormons] and subject to the governance of Vermont native Brigham Young, who was opposed to the practices of Southern slavery.”

Until Congress erased slavery in all the territories in 1862, Young, the Mormon prophet, and the fledgling Church of Jesus Christ of Latter-day Saints struggled to find compromise between members’ general opposition to slavery and its practice in Utah.

Thiriot’s research focuses on five Southern families who migrated to the territory, bringing 99 African-American slaves with them.

One of them was Green Flake, who had accompanied other slaves owned by Mississippians James and Agnes Flake first to Nauvoo, Ill., and then on to Utah as part of the Mormon migration. Stories have been told about Green Flake being donated as tithing to the LDS Church, and Young in particular, by the then-widowed Agnes Flake.

Thiriot has serious doubts about those tales. She argues that her research indicates that the widow “hired him out to Brigham Young for a year to solve a complex problem that involved her family’s poverty.”

“Green Flake worked for him about a year and then became a freeman,” she says. “One of the interesting things I found during my research is that the descendants of the enslaved . . . almost uniformly recalled that their families loved and respected Brigham Young.”

Flake, who had been baptized into the LDS Church in 1844 and drove the wagon that brought Young into the Salt Lake Valley in 1847, was freed by Young in 1854 after a year’s personal service to the leader. After his wife died, Flake moved in 1885 to Idaho, where he joined his children and grandchildren. He died in 1903.

Flake is one of a dozen African-American Utah pioneers Thiriot plans to highlight during her free presentation Thursday.

Thiriot, a Brigham Young University history graduate, has written and spoken extensively on genealogical research, particularly stories of 19th- and early 20th-century Latter-day Saints.

She is working on a book for University of Utah Press tentatively titled “Slaves in Zion: African American Servitude in Utah Territory, 1847-1862.”

(Tribune file photo) A reproduction of an 1897 Tribune woodcut of Green Flake, one of nearly 100 slaves brought to Utah in pre-Civil War days.