Napoleon's response to the Hen Rebellion represents Stalin's Great Purge.
About halfway through, Animal Farm takes a dark turn. The hens refuse to give up their eggs; Napoleon starves them; several of the hens die; the rest simply give up.
But it doesn't end there.
Soon after, Napoleon calls a general meeting, and the dogs drag out several pigs "squealing with pain and terror" (7.24). The pigs confess that they were working with Snowball and Mr. Frederick, and a moment later the dogs "tore their throats out" (7.25). And then it happens again, with hens from the rebellion, a goose, and several sheep. At the end, there's "a pile of corpses and Napoleon's feet and the air was heavy with the smell of blood, which had been unknown there since the expulsion of Jones" (7.26). Um, wasn't this supposed to be a fairy tale?
Not exactly. What we have here is a nightmarish allusion to the Great Purge, which took place between 1936 and 1938. To eliminate his opposition, Stalin executed or exiled anyone he didn't like: Trotsky's supporters, as well as landowners, military leaders, and Jimmy Buffet fans.
Okay, we made that last one up.
The point is, Stalin went a little nuts "purging" the Soviet Union of its perceived enemies. The estimates of how many died in the purges ranges from about 500,000 up to 2 million. And they had a particularly nasty element: Stalin forced people to confess falsely and publicly to crimes that they never committed, often after psychological torment and outright torture. These became known as the "Moscow Show Trials."
Animal Farm has its own set of show trials: Squealer tells the other animals that Snowball isn't just working against them from outside the farm, but that he's sneaking back to destroy them from within. General Stalinist paranoia becomes a good old-fashioned witch-hunt, plain and simple.