It is ironic that while Napoleon has fought with the other animals and Snowball to free themselves from human control, it is the burgeoning human traits in him that lead to his corruption as an animal as in his rapacity he vies with Snowball for power.
According to Napoleon, what the animals must do was to procure firearms and train themselves....According to Snowball, they must send out more and more pigeons and stir up rebellion among the animals on the other farms. (Ch.5,par.12)
In Orwell's allegory, Napoleon's behavior here mimics that of Joseph Stalin in his power struggle against Leon Trotsky, who wanted a Permanent Revolution throughout--as Snowball wants the other animals to overthrow their owners--whereas Stalin wanted Socialism in one country while promising to empower the people (the animals).
After running Snowball off, Napoleon begins a program of propaganda. This effort to control all the animals, even to the point of exploiting other animals, such as Squealer who becomes his propagandist and the "nine enormous dogs wearing brass-studded collars," becomes more and more ruthless as he eliminates anyone who opposes him. For instance, after Napoleon becomes the leader, he announces that there will be no more debates; Squealer "explains,"
No one believes more firmly than Comrade Napoleon that all animals are equal. He would be only too happy to let you make your decisions for yourselves. But sometimes you might makes the wrong decisions....Suppose you had decided to follow Snowball,...who, as we now know, was no better than a criminal?
In another instance of Napoleon's propaganda, Squealer clarifies the reason for Napoleon's decision to build the windmill after all.
He had seemed to oppose the windmill, simply as a manoeuvre to get rid of Snowball, who was a dangerous character and a bad influence. (5, last par.)
These actions also mimic Stalin who used the "pogroms" against those who were allied to old powers or were not slavish to his ideology. To further his designs, Napoleon enlists the unintelligent sheep and has them chanting his political sayings when other animals raise objections, as, for example, after he does away with meetings.
The four young pigs who had protested...raised their voices timidly, but they were promptly silenced by the growling dogs. Then, as usual, the sheep broke into "Four legs good, two legs bad!" (6.7)
As with all who seize power, corruption takes place more and more in Napoleon. Gradually, the Commandments are altered to fit the designs of Napoleon. For example, the Fifth Commandment was "No animal shall drink alcohol," but after Napoleon starts to imitate humans and gets drunk at the end of Chapter 8, Muriel finds words she does not remember, for the Commandment reads, "No animal shall drink alcohol to excess."
Then, in Chapter 9, Napoleon is installed as "President." He moves into Jones's house and, like Stalin, has those who oppose him or are no longer useful, killed, such as Boxer when he can no longer work. Finally, the animals see what they would never have imagined. "It was a pig walking on his hind legs." Corrupted by his power, Napoleon has assumed the role of the oppressor, the human being.