By retelling the story of the Russian Revolution and its aftermath in the form of a "Beast Fable," or a story where animals have the power of speech and abstract reasoning, George Orwell was able to satirize Communism without resorting to long historical or geographical explanations. The structure of a working farm is similar to that of a country under dictatorship or royal rule, and so it lent itself well to satirizing the Russian Revolution:
"Is it not crystal clear, then, comrades, that all the evils of this life of ours spring from the tyranny of human beings? Only get rid of Man, and the produce of our labour would be our own. Almost overnight we could become rich and free."
(Orwell, Animal Farm, msxnet.org)
The teachings of Old Major are almost identical to those of Karl Marx, but scaled to a smaller level; if animals can remove their human masters (if the proletariat can remove the bourgeoisie), then they can work only for their own benefit and not support a lazy upper-class who take and never give back. The animals, then, are perfect representations of the undereducated working class of Russia, who labored in vain for a better tomorrow for the benefits first of a royalty, and then for a ruling dictatorship that told unashamed lies about their success and the benefits for the working class.
According to the British Library, the Beast Fable is a style of story in which the author endows animal characters with human qualities. By doing this, a Beast Fable allows the reader to "examine their behaviour from a distanced perspective."
In Animal Farm, Orwell uses the Beast Fable to comment on the Russian Revolution and the style of government which followed. In Chapter One, for example, Orwell uses the character of Old Major as a representation of Vladimir Lenin, a revolutionary who provided the ideological impetus for the revolution. Later, through the characters of Snowball and Napoleon, Orwell portrays the power struggle between Leon Trotsky and Joseph Stalin, two of the revolution's leaders. Snowball's exile from the farm, for instance, is symbolic of Trotsky's exile from Russia in 1928. This enabled Stalin to claim absolute power, just as Napoleon does after Snowball is removed.
By using this style of fable, Orwell makes an important point about the Russian Revolution. Specifically, that the Communists who pledged to make the people free were, in fact, just as tyrannical as those who ruled before.