Orwell's wonderful tale depicts the utter failure of the Russian Revolution and the betrayal of its purpose by its leaders. The premise of the Revolution was to ensure equality for all. Its goal was to uplift those who were victims of a system of abuse and prejudice and to ensure that each citizen directly shared in the wealth and privilege which had been the preserve of the privileged few--the Russian aristocracy and upper class.
The novel, furthermore, exposes how power corrupts over time. After the Rebellion, the pigs, who had assumed leadership, almost immediately begin abusing their authority to benefit themselves, to the exclusion of all others. They use the milk to mix into their mash and claim the windfall apples for themselves. On a question as to why they have done so, they use propaganda, fear, and misinformation to easily convince the largely unintelligent general animal populace. Squealer tells them that they need the sustenance provided by the milk and apples to effectively perform their task of running the farm, otherwise Jones will come back.
This response to the animals' queries becomes a trend. Whenever the pigs change a commandment, they use Squealer's excellent oratory to persuade the animals that they are not doing anything wrong, and that they are acting in everyone's best interests. The pigs' sly tactics quickly lead to much more extreme action. Napoleon expels Snowball from the farm and later has some animals slaughtered by his vicious dogs under the pretext that they have been betraying their comrades by trying to destroy whatever has been achieved. An atmosphere of fear and anxiety now permeates every aspect of the animals' lives.
By using these incidents, Orwell illustrates how Joseph Stalin assumed leadership and became a dictator. Just like Napoleon, Stalin also used brutal measures to get rid of his enemies. He, for example, had Leon Trotsky exiled, just as Napoleon has done with Snowball. Once Snowball is gone, Napoleon becomes a dictator and imposes tyrannical rule on the animals. All the original ideals of Animalism are quickly forgotten and the pigs assume human characteristics and indulge in human behavior. Napoleon's absolute authority has corrupted him absolutely.
At the end of the novel, all the original commandments are replaced by a single paradoxical tenet:
All animals are equal but some animals are more equal than others
The pigs start walking on their hind legs and carry whips in their trotters. Napoleon starts wearing clothes and begins smoking a pipe. When the animals see him conversing with humans during a meeting, he cannot be distinguished from the humans, as the following excerpt indicates:
The creatures outside looked from pig to man, and from man to pig, and from pig to man again; but already it was impossible to say which was which.
Things on the farm have come full circle. The Rebellion has been a disaster that only succeeded in ensconcing the pigs in the same positions of entitlement that Mr. Jones and his men had occupied. The ironic difference is that now, the abuses, exploitation, and oppression of the animals are imposed upon them by their own kind and not by some uncaring and ruthless humans. Stalin and his cronies had, similarly, enslaved their comrades and exercised their brutality on them.