Animal Farm is a scathing critique of the Russian Revolution and Soviet Communism, but at its heart, like many of Orwell's works, it is a critique of dictatorship. The story itself shows the gullible nature of people and the ease with which movements and governments are subverted and destroyed. Orwell, who was a socialist, wrote the story as a cautionary tale for anyone who held up Soviet Russia, the Russian Revolution, or Communism as examples to follow.
In a letter to his friend Dwight Macdonald, written in 1946, Orwell explains that:
What I was trying to say was, "You can't have a revolution unless you make it for yourself; there is no such thing as a benevolent dictat[or]ship. . . ."
From Orwell's perspective, it was necessary to point out that revolutions, which he wasn't necessarily against, would only work if they evolved organically. At the start of the story, when the animals overthrow the farmer and establish "animalism," the rules and systems of their society come from the power and authority of the revolution and the animals themselves.
However, once the pigs take charge and the animals let them, there is little hope for anyone on the farm. The myth of the benevolent dictator, something that seems prevalent in all forms of communism, is thoroughly dismantled in Animal Farm. Orwell shows the dangers of dictatorship and the shifting narrative of a communist system that replaces the revolutionary government, pointing out with clarity the flaws in such systems.