A central theme in both Lord of the Flies and Animal Farm is the transition and corruption of power. In both books power is transferred from a pre-existing system to a new leader, and from there, the power is taken by another leader who is more appealing to those under him, but is quick to act upon violence and does not work towards the common good of all. In Lord of the Flies this is exemplified through Ralph, Jack, and the lack of adults on the island.
As schoolboys, before crashing onto the island, they had always looked to adults to lead and be the power in place, but they no longer have that. When Ralph becomes the elected chief he becomes the new power, but there are obvious tensions between him and Jack immediately. Ralph is focused on surviving, building shelter, finding food, and hopefully, getting rescued at some point. Jack and many of the other boys are enjoying the absence of adults on the island and are focused on hunting pigs, swimming, and just having fun. As the story goes on this drives the boys to abandon Ralph's leadership and to follow Jack, who quickly turns violent. He tortures Wilfred while claiming that Ralph and his group are a danger to the tribe, mimicking Napoleon as he chases Snowball off the farm in Animal Farm. Towards the very end of the book, when Roger drops the boulder on Piggy, he does so because he knows he can, and there is nobody on the island to limit his call to cruelty.
The power in Lord of the Flies is very tentative. The conch shell was meant to give everybody the ability to speak in assembly, but that power was taken from Piggy, who was ignored and told to shut up even when he had the conch in hand. Ralph's power is taken by the group when they no longer cosign his ideals of survival, rescue, and order. When Roger drops the boulder on Piggy, killing him and crushing the conch shell, it symbolizes the total loss of power once held by anyone on the island. At the time when Jack is in charge, throwing spears at Ralph, and watching Piggy get dropped off a cliff, the island is a free for all. Throughout the story, power changes through many hands, and is transformed from a force of good, to a force of chaos.
In Animal Farm, the preexisting state is Mr. Jones' rule of the farm. After he is chased off the farm, the animals take control and Snowball and Napoleon start calling the shots. They butt heads on a lot of the issues surrounding the farm, and their relationship looks very similar to that of Ralph and Jack. Later in the story as the two pigs argue over the construction of the windmill their motives are apparent. Snowball is thinking of the other animals on the farm, while Napoleon is thinking only about himself and the profits of the farm. Napoleon knows Snowball is right in his quest to build the windmill for the farm and he is scared of the support that Snowball has, he views him as an enemy, and therefore has to have him chased off the farm.
After Snowball is chased from the farm the conditions quickly begin to deteriorate. Napoleon and Squealer take the power for themselves and begin to manipulate the commandments of the original constitution set forth when Animal Farm was created. Those commandments, which were once a source of order and equality, were corrupted to be a source of power for the pigs only. In both Lord of the Flies and Animal Farm, the original source of power is corrupted to a point where it is no longer what it was meant to be. Both books give a light to the idea that change is not always good, and power in the wrong hands corrupts and destroys ideals.