Are you going to watch ‘American Primeval’? Let us explain a key moment: the Mountain Meadows Massacre.

The first episode of the new Netflix series “American Primeval,” which premieres Thursday, depicts the horrific assault of Sept. 11.

No, not the terror attacks that stunned New York, Washington and Pennsylvania in 2001 — rather, it portrays the gory rampage that rocked southern Utah 144 years earlier.

It came to be known as the Mountain Meadows Massacre and still stands as the bloodiest stain on the history of The Church of Jesus Christ of Latter-day Saints.

Here, in brief, is what happened and how you can learn more about the violent attack:

It took place at a time of heightened tensions after the federal government, wary of the Brigham Young-led theocracy in place, sent troops to the Utah Territory. For their part, Latter-day Saints, fearing war, grew distrustful of any outsiders.

When a wagon train of emigrants en route from Arkansas to California passed through, Mormon militiamen laid siege to the company. Then, on and about Sept. 11, 1857, they waved a flag of truce. But instead of talking, militia gunners mercilessly slaughtered more than 100 men, women and children.

“What was done here long ago by members of our church represents a terrible and inexcusable departure from Christian teaching and conduct,” senior Latter-day Saint apostle Henry B. Eyring said during a 2007 visit to the southwestern Utah site. “We cannot change what happened, but we can remember and honor those who were killed here.”

John D. Lee was the only person ever convicted and put to death for his part in the carnage. He was executed March 23, 1877, by a firing squad at the site and buried in Panguitch.

To understand more about the heinous crime — the anxieties that led to it, the cover-up that followed and the efforts to make amends ever since — you can read these stories from The Salt Lake Tribune and listen to these “Mormon Land” podcasts.

• Historian Richard E. Turley Jr., who co-wrote the highly acclaimed “Massacre at Mountain Meadows: An American Tragedy,” talks about the mass killings in this story and an accompanying podcast. You will learn about the high-level hoops the authors had to jump through to gain full access to all the church documents. “What I saw,” Turley recalls, “was terrible.”

• In a follow-up volume, “Vengeance Is Mine: The Mountain Meadows Massacre and Its Aftermath,” Turley teams up with Barbara Jones Brown to examine how church leaders in southern Utah tried to hide the atrocity, how investigations were thwarted, how justice was delayed and denied, and how some men were haunted for decades by their involvement. The authors also explore a key Watergate-like question: What did Brigham Young, the church’s prophet-president at the time, know and when did he know it? Listen to the podcast and/or read excerpts from the interview.

• See how Latter-day Saints and their top leaders have slowly but steadily mended relations with descendants of the massacre victims.

• On the 150th anniversary, the Utah-based faith, in a tearful and solemn ceremony, issued what has been termed an “apology.” Read the full statement from the church’s governing First Presidency.

• The massacre site is named a national historic landmark.

• In 2017, the skull of an unknown child victim was buried at the former killing fields, and, in 2023, a search was planned for finding more possible graves.

• Read about Juanita Brooks, the 20th-century Latter-day Saint historian who was roundly criticized during her life but widely praised after her death for telling the unvarnished story about the bloodbath in her seminal 1950 book titled simply “The Mountain Meadows Massacre.”