The two ways in which history has been altered in this dystopian society are through its war against books and its attempt to destroy them completely. This has been achieved in part through the triumph of mass media and the TV shows that Mildred and her friends are so partial too. Note how the power of TV shows and mass media are compared to that of books in the following quote:
Books can be beaten down with reason. But with all my knowledge and scepticism, I have never been able to argue with a one-hundred-piece symphony orchestra, full colour, three dimensions, and I being in and part of those incredible parlours.
The TV parlours are so powerful and mighty because they completely overwhelm those who watch them in an unstoppable wave of sensual description, making them impossible to fight against, whereas, by contrast, books can be "beaten down with reason." History has thus been changed profoundly through the destruction of books and the triumph of mass media. Linked to this, another way in which history has been changed is demonstrated through Montag's surprise that the fire department ever existed to do anything else except burn books. He, and presumably society, has forgotten, or never knew, that the fire department actually existed to put out fires and to stop things from burning, whereas in the novel, the opposite is true. The way in which the totalitarian government tries to dominate history and change it, particularly in the perceptions of its citizens, is a very disturbing element to this dystopian novel.