"We don't worship so much as follow a set of principles. We want to bring peace back to this wasteland. The world tends toward destruction, so we try to make a difference.”
—Nicole

History:

Sickness was spreading in San Diego (later renamed Dayglow), the only remaining town near the Glow, so Nicole and her parents gathered all the people and organized an exodus to the north. During the travel, however, her parents were killed by marauders. Tired of the killing and motivated by the death of her parents, she founded the Followers of the Apocalypse, dedicated to reeducating and rebuilding the wasteland and to ensuring that humanity does not repeat the mistakes that led to the Great War.

After their creation, they continued traveling to the north and settled in the Boneyard, establishing a headquarters in the former Los Angeles Public Library. The Followers are generally liked where they go, since they teach people valuable medical and agricultural knowledge. Around 2161, they were one of the few groups to recognize that the Children of the Cathedral were more than what they seemed, and were suspicious of their motives. Talius, a ghoul-like mutant partially exposed to FEV by the Master's forces, found refuge among the Followers, and helped them understand the true nature of the Children.

After the death of the Master, the Boneyard became one of the states of the New California Republic, and the Followers became both a major influence in the newly-founded NCR and the controlling organization in the Boneyard. Growing in power, the Followers begin to create expeditions to bring peace everywhere in the Wasteland. Some were disappointed with the choice of being allied with the NCR and left the Followers, while keeping and trying to inculcate the principles (Vidya had left to go to the town of Carbon in Texas, to inculcate the Followers doctrine in her own way).

The most important expedition was to the Mojave Wasteland where, with the help of the NCR, they traveled into New Vegas, settling in the Old Mormon Fort in Freeside where they could tend to the wretched and downtrodden. They took in stragglers of many creeds and colors, including the last few Enclave remnants. Despite the historic name of the place, there are no serious fortifications - just fences and gates with a few armed Followers inside. Over time, relations between the Followers and the NCR Senate turned sour. NCR broke most ties with the Followers, and turned their support to their own OSI.

The Followers are touchy about their connection with Caesar’s Legion, a powerful slaver group east of the Colorado River. It is from their ranks that Edward Sallow, now known as Caesar, the founder and leader of the Legion, came.

Society:

The Followers' goal is to bring the torch of knowledge to the wastes and facilitate the free flow of information, technology, and supplies equally among all the peoples of the wasteland. They often provide education, medicine, and scientific expertise free to all who require it and their members are frequently found lending their aid to the needy wherever they can. Ideologically, the Followers' principles bear some resemblance to anarchism - above all else, they support pacifism and cooperation. They oppose organizations and civilizations which seek to thwart these principles, albeit not through violent means.

Following the NCR's arrival in the Mojave, relations between the Followers and the NCR Senate turned sour. NCR broke most ties with the Followers, and turned their support to their own OSI. The Followers don't care about controlling territory, unlike NCR, but rather concern themselves with the welfare of the people. It is said by Ignacio Rivas at the HELIOS One solar plant, that they tend to "clean up" after the NCR.

Relations with the outside:

The Followers are generally liked where they go, since they teach people valuable medical and agricultural knowledge. However, some governments dislike the Followers, as they are generally liberal thinkers who occasionally plant seditious thoughts in the heads of oppressed citizens. The Followers are also touchy about their connection with Caesar's Legion, a powerful slaver group of the east. It is from their ranks that the original Caesar came.

https://boards.ign.com/teh_vestibule/b5296/197488926/p1/
(Followers' interesting relationship with Brotherhood of Steel)

Technology:

While the Followers of the Apocalypse's technology is remarkable and their technological knowledge is excellent, they don't have the means to replicate it or improve drastically upon it. Thus they usually have to depend on what they can scavenge or repair around them. These limitations largely hold them back from their main goal and from spreading their message to other parts of the Wasteland.