George Orwell's novella Animal Farm is an allegory (he called it a kind of fairy tale) in which the events and characters in the novel are a direct reflection of a certain place at a certain time. Animal Farm is Russia (the USSR), and the leaders on Animal Farm are the leaders of Russia in the first half of the twentieth century.
After the animal stage their impromptu rebellion, things on the farm are good for awhile, though even from the beginning the pigs are more powerful than the rest of the animals. The two pigs who are most powerful are Snowball (representing Leon Trotsky) and Napoleon (representing Joseph Stalin). Of course we know that Napoleon chased Snowball off the farm by force, so by the time the farm needs to have an elected leader, the animals are not left with many choices:
In April, Animal Farm was proclaimed a Republic, and it became necessary to elect a President. There was only one candidate, Napoleon, who was elected unanimously.