Animal Farm by George Orwell is a short novel or novella first published in England on 17 August 1945. This book tells the story of animals that rebel against their human farmer, hoping to create a society where the animals can be equal, free, and happy (utopia). Ultimately, the rebellion is betrayed, and the farm ends up in a state as bad as it was before. Animal Farm is an allegory and satire about the Russian revolution from its roots in the theories of Karl Marx to its actualization by Leon Trotsky and Joseph Stalin.
In other words, Animal Farm is a condemnation of Joseph Stalin and all other Soviet Union leaders who betrayed what everyone was fighting for-Socialism. After seizing power, those leaders (especially Stalin=Napoleon) monopolized power and thus introduced a totalitarian system in which they killed anyone who did not follow their way.