At the beginning of the book, the worst enemies of the animals are obviously the humans, specifically Jones. By the end of the book, the animals are indistinguishable from the humans. In between, we watch as the pigs, having led the revolution, use their power for self-aggrandizement rather than the good of the society as a whole. Yet the process is that of a gradual corruption. The pigs have, or at least seem to have, the interests of the whole farm at heart in the beginning when they extrapolate Old Major's teachings into Animalism. While the pigs certainly are the enemies of their fellow animals by the end of the book, it is the corruption that comes with unchecked power that makes them that way. This corruption is made clear both by the scene at the end of the book when the animals are unable to tell the difference between the pigs and the humans, as well as the alteration of the Seven Commandments to read that "some animals are more equal than others."