The meeting between the pigs and humans at the end of Animal Farm alludes to the Tehran Conference of 1943 and the beginning of the Cold War.
At the end of the novel, the animals peek through a farmhouse window as the pigs explain to the humans that there must have been some misunderstanding. See, they never meant to incite rebellion; their entire goal has been "to live at peace and in normal business relations" (10.27).
A.k.a., the rebellion is dead. "Normal business relations" is code for capitalism—at least, capitalism in relation to the rest of the world. Behind this farmhouse meeting is the Tehran Conference, a November 1943 meeting between the World War II Allied leaders Franklin Roosevelt (U.S.), Winston Churchill (U.K.), and… Dear Leader Stalin himself (U.S.S.R.).
At this point in the war, Stalin's army was looking pretty successful, and the other leaders wanted his help. In exchange, he got them to promise to support his government and also to give him most of eastern Poland. Churchill and Roosevelt decided that Stalin's demands were a small price to pay for winning the war. But plenty of other people in the West—like Orwell—saw it as a sellout at best and a compromise with an evil dictator at worst.
No wonder we end on this line: "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" (10.32).
That's how we know Animal Farm is more than a simple anti-communist allegory. It's an anti-everything allegory. The pigs and men are identical, and they're both cheating each other: "Napoleon and Mr. Pilkington had each played an ace of spades simultaneously" (10.32).
The moment that ace of spades hits the table is the allegorical beginning of the Cold War, a decade-long mostly non-military conflict between the U.S.S.R. and the U.S. that was so tense that kids in both countries had nuclear bomb drills at school. (Ask your grandparents.)
In 1941, the leaders the Allied countries were willing to compromise with Stalin. Maybe they even believed he wasn't so bad. But not Orwell. Orwell could see the cards on the table.