How can this book serve as a warning to people?

Animal Farm is an allegory or fable, a fairy tale for adults. Orwell uses animal characters in order to draw the reader away from the world of current events into a fantasy space where the reader can grasp ideas and principles more crisply. At the same time, Orwell personifies the animals in the tradition of allegory so that they symbolize real historical figures. In their own universe, people can become desensitized even to terrible things like deception, mistreatment, and violence. By demonstrating how these things occur in an allegorical world, Orwell makes them more clearly understood in the real world. For instance, in Animal Farm’s public execution, Orwell lays bare the matter of execution by having the dogs rip out the supposed traitors’ throats. In this scene, the reader is led to focus not as much on the means of execution as on the animalistic, atrocious reality of execution itself.