Beatty explains that the history of the firemen began around the Civil War. At that point, society quickly began changing, which was amplified by new technologies like the camera, radio, and television. As television became more popular, people no longer had the stamina to read long books, so it became normal to deliver greatly condensed versions of works like Hamlet so that people could get just the main idea.
Academic learning was dismissed. People were not trained to think but instead were simply trained to press buttons and pull switches at their jobs. And still, the threats inherent in books loomed for various populations. It became important that no work reflect any kind of controversy for any population anywhere. Authors became cognizant of this fact and simply stopped writing. A "blend of vanilla tapioca" was all that remained of publications.
Books became the metaphorical "loaded gun" in society, threatening the "happiness" of its members. Beatty says that a "well-read man" is a threat and that he "won't stomach them for a minute." This is where the role of firemen transformed.
Society needed someone to ensure the "peace of mind" of its members. It looked to avoid the "rightful dread of being inferior," so firemen became the "judges and executioners" to rid the world of this threat.
In this society, people simply want to be happy. They don't want to feel threatened or to question their sense of equality. They don't want to be troubled with complex ideas or with unhappy realities of the past. Therefore, firemen are charged with rooting out hidden literature where they find it, burning all copies of these "troublesome" works so that society can remain blissfully content. To make the point crystal clear, the firemen are also charged with burning the entire home where they find those books, instilling a sense of fear among those who might try to circumvent the law.
The ability for the firemen to exist as they are in Montag's society, as men who burn books, was paved long before that job existed. Society paved the way for firemen to be possible. Beatty explains the road leading up to firemen when he visits Montag's house the morning Montag stays home sick (after they burn Mrs. Blake with her books). Beatty explains that people got tired of reading so much, of putting so much effort into reading, so books got shorter and shorter, and finally people just stopped writing them because no one bought them or read them. So that is one factor. Another is that so many people were offended by the various content of books, that they started banning them, censoring them, and sometimes even burning them themselves. They were offended by them, so reading them became the uncool thing to do; if you read those hate-mongering books, you were a racist, or insensitive, or prejudiced. Also, if you read books you were considered snobby because you made people who didn't read look and feel stupid. The stigma placed on you if you read books was so uncomfortable that people stopped reading to avoid being made fun of and ostracized. So, books became unpopular in that way. All of that paved the way for firemen.
Montag asks at one point, "in the old days, before homes were completely fireproofed--" whether firemen prevented fires instead of starting them. So, they bust out the rule book, which states that the first fireman was Benjamin Franklin who, in 1790, burned "English-influenced books in the Colonies." It's an interesting assertion. Then, the rules state:
"1. Answer the alarm swiftly. 2. Start the fire swiftly. 3. Burn everything. 4. Report back to the firehouse immediately. 5. Stand alert for other alarms."
So, pretty simple rules there, but getting to the point where firemen became what they were, required a long, slow process that was forged by society's apathy and political correctness, along with modern technology that made homes "fireproof". I hope those thoughts help! Good luck!