The Church Universal and Triumphant, founded in 1975 by Elizabeth Clare Prophet, once had thousands of members.
Prophet's followers, who called her "Mother" were entranced by her hypnotizing personality and claims to be a channel for ascended beings. Prophet pulled teachings and ideas from Christianity, Buddhism, and mysticism along with the teachings of several theosophists. Believers worshipped her and gave her money and support.
Eventually, Prophet began telling her followers that the end of the world would come in 1990 when a nuclear war would break out between Russia and the United States.
She told them that the only place to be safe was at a compound near the cult's headquarters — the former Malcolm Forbes Ranch — in Gardiner, Montana. It was located just outside Yellowstone National Park.
"People moved there from all over the US and world. They brought money they brought everything," Rick Ross, executive director of the Cult Education Institute, told Insider. "They built bomb shelters, which still exist to this day."
Ross, who has studied cults since the 1980s, is an expert witness on the subject and has worked with law enforcement around the country. He also wrote a book on the subject, entitled, "Cults Inside Out: How People Get in and Can Get Out."
Ross recalled the late 1980s when individuals called him concerned about their loved ones who gave up everything to move to the property and worship Prophet. Montana residents were also concerned with what would happen at the property, where thousands had stockpiled weapons, food and supplies in preparation for Armageddon.
Well, needless to say, the world didn't end. And unlike David Koresh's Branch Davidians or the Heaven's Gate cult, the Church of the Universal and Triumphant petered out peacefully.
When the prophecy failed, the church began to shrink. In the late 1990s, Prophet was reportedly diagnosed with Alzheimer's and stopped speaking publicly. Other people spoke for her until her death in 2009, Ross said.
Eventually, after that, the considerable assets of the cult were sold off and the organization disintegrated. Prophet's children didn't want a role in the group, according to Ross.
"There were people who left that created splinter groups, some of those still exist," Ross said. "Some of them are in the area of the original ranch near Billings, Montana, and Yellowstone."
The numbers, though, are nothing what they once were. These smaller groups may have between 100 or 200 followers, Ross said.
"This is what happens with many groups that are personality-driven," Ross said. "It's like a wheel, the leader is the hub of the wheel."
When the leader dies, the hub of the wheel falls off, and the group can't carry on, he said.
But the fall of Church Universal and Triumphant (CUT) is far from the end of the doomsday movement. The church's teachings live on via the Summit Lighthouse, CUT's publishing arm. Prepping for the end of the world has become a popular online subject and also a big business.
The movement has also seen a resurgence of interest following the disappearance of two Idaho children whose mother, Lori Vallow, is believed to have ties to the doomsday network "Preparing A People." Vallow recently married Chad Daybell, a doomsday author, and both of them have claimed to have received prophecies.
"Lori Vallow and Chad Daybell are very much not part of the Church Universal and Triumphant," Rick Ross told Insider confidently.
For them, their doomsday tendencies stem from a distorted view of Mormon beliefs, said Ross, who is following the case closely.
Still, like CUT, Ross has gotten several calls from people concerned about their loved one's involvement in Preparing A People.
"Many of the people on this online network called Preparing a People are tied to the LSD [Latter Day Saints] church, but the beliefs they express are not typical of Mormons," Ross said.
Concerned people have told Ross that the followers are "obsessively stockpiling food, water and are talking alarmingly about the end being near."
When news of the disappearance of Vallow's children, Tylee Ryan, 17, and J.J. Vallow, 7, surfaced, Preparing A People tried to distance themselves from the couple.
Vallow's fourth husband, Charles Vallow, her brother Alex Cox, and Daybell's former wife Tammy, have all died within the past nine months. Police in multiple states are investigating the string of deaths.
There is also an ongoing investigation into the attempted killing of Brandon Boudreaux, who was married to Lori Vallow's niece, Melani Boudreaux. Boudreaux said that Melani and Lori's involvement in "a cult" ruined their marriage and has alleged that his ex-wife knows where the missing children are, but isn't cooperating with police.
In a statement, Preparing A People said that it wasn't a cult.
"We also do not share any of Chad Daybell's or Lori Vallow's beliefs if they are contrary to Christian principles of honesty, integrity, and truth, or if they do not align with the doctrines of The Church of Jesus Christ of Latter-day Saints," the statement said.
J.J. Vallow and Tylee Ryan have both been missing since September. Vallow and Daybell have not cooperated with police and fled their Idaho home in November after police came to do a well-being check on JJ, who is autistic.
The couple fled to Hawaii the next day.
Last month, a judge ordered Vallow to turn her children over to the state of Idaho. Vallow failed to deliver the children, and on Thursday she was arrested in Kauai and taken to the Kauai Community Corrections Center where she is being held on a $5 million bond. She has been charged with two felony counts of desertion and nonsupport of children, along with resisting and/or obstructing an officer, solicitation, and contempt.
Police are continuing their search for both of the children.
Tylee was last seen on September 8, when she, J.J., Vallow and Vallow's brother Alex Cox went on a day trip to Yellowstone National Park.
JJ was seen playing in his yard in Idaho a week later but was then unenrolled from school.
Investigators are considering searching inside Yellowstone National Park for Tylee, sources close to the investigation told CBS News.
Gary Hagen, Assistant Police Chief in Rexburg, Idaho, declined to confirm to Insider whether investigators were searching Yellowstone or have been looking at other doomsday groups in the area for leads.