Napoleon gains power over Animal Farm first and foremost by careful planning. As early as chapter 3, when the other animals are busying themselves with the harvest and Snowball is organizing committees, Napoleon quietly appropriates Jessie and Bluebell's nine puppies and takes them to a loft where he keeps them in seclusion until they are grown. It may be that if Napoleon's campaign "Vote for Napoleon and the full manger" had been successful, he would not have used the dogs against Snowball in chapter 5. Probably he would have found occasion to call on them sooner or later in any case. The point is that he had a back-up plan in case Snowball won the popular vote and that this plan was conceived a long time in advance.
Once Napoleon has gained power through planning and the use of force, he uses more force and propaganda to maintain it. The dogs are always there, ready to treat any dissidents in the same way as Snowball. The pattern is set immediately after Snowball's expulsion. When four of the pigs spring to their feet to protest against Napoleon's new regime, the dogs growl and the pigs promptly sit down. Then the sheep begin a chorus of "Four legs good, two legs bad," which silences any further discussion. And, soon afterwards, Squealer is sent round to feed the party line to all the animals on the farm. This combination of latent force and propaganda is repeated throughout the remainder of the book.
Napoleon gains power over Animal Farm by executing an effective plan to expel Snowball, intimidate his subjects, and utilize persuasive propaganda to manipulate the less intelligent animals. Napoleon begins his plan to control the farm by taking Jessie and Bluebell's nine puppies and raising them in the loft of the barn. Napoleon understands the importance of ruling with force, and he indoctrinates the nine puppies in seclusion. As the puppies grow and develop into ferocious, loyal dogs, Napoleon campaigns against Snowball and his popular ideas. Unlike Snowball, Napoleon focuses on the less intelligent animals for support and teaches the sheep to interrupt Snowball's speeches.
Napoleon recognizes that Snowball poses a threat to his authority and gets rid of his competition by sending his nine ferocious dogs after him during a meeting in the barn. Once Snowball is driven from the farm, Napoleon proceeds to cancel all Sunday meetings, places the pigs in charge of developing new policies, and assumes the position of dictator. Napoleon then employs Squealer to distort the truth and manipulate the other animals by using effective propaganda techniques.
Squealer threatens the animals with Jones's return, dramatically inflates Napoleon's accomplishments, uses Snowball as a scapegoat, and convinces the animals that the standard of living has risen since Napoleon took over. Napoleon also develops a cult of personality, alters the history of the farm, and amends the principles of Animalism to align with his self-serving policies. The animals suffer under Napoleon's reign and live in constant fear after he publicly executes dissenters and reduces their food rations. Napoleon is able to maintain his power by subjecting the animals to effective propaganda, keeping the standard of living on the farm extremely low, and using fear tactics to control them.
Napoleon and the pigs initially begin to manipulate the tenets of Animalism in their favor. As a pig, Napoleon enjoys special privileges and is viewed as a leading authority figure throughout the farm. In chapter 5, Napoleon usurps power by releasing his nine ferocious dogs after Snowball and convincing the other animals that Snowball is a traitor. Napoleon then begins to spread false propaganda through his public speaker named Squealer. Squealer distorts the tenets of Animalism to coincide with Napoleon's actions and continually warns the animals about Jones's return. Napoleon's tyrannical reign continues as he begins to engage in trade with humans, uses Snowball as a scapegoat, abolishes the song "Beasts of England," and publicly executes dissidents. Napoleon ruthlessly forces various animals to falsely confess to crimes against the farm before murdering them, which creates an atmosphere of fear and hysteria throughout the farm. Napoleon also makes the animals rely on him for food and gives himself the title "Our Leader, Comrade Napoleon." Napoleon then distances himself from the other animals and begins dressing like a human. His superior status, continued propaganda, oppressive nature, and exclusivity certifies his leadership and reign over Animal Farm.
Napoleon gains power over the animals by two means. First, he twists the ideas of the animals' revolution to suggest that questioning his authority is tantamount to treason to Animal Farm, and the good of the whole. This is part of his larger strategy of manipulation of the truth. Squealer, his "propaganda minister," is especially adept at getting the animals to believe whatever is necessary to promote Napoleon's power. After Napoleon drives Snowball from the farm, for example, it is Squealer who convinces the animals that constructing the windmill was actually Napoleon's idea (even though Snowball had publicly endorsed it against Napoleon's wishes). He further suggests that Snowball, who had in fact fought bravely in the battles to establish Animal Farm, had in fact been in league with Jones, the farmer, the whole time. Snowball's ability to twist information is best exemplified by the winnowing down of the original Seven Commandments to one, which claims that while all animals are equal, some animals "are more equal than others."
The other means by which Napoleon maintains power is terror. We see this most clearly when he uses the dogs to massacre dozens of animals in the barnyard, each of which is accused of (indeed many freely confess to) treason against the farm. This bloodletting is meant to remind readers of the bloody purges of Joseph Stalin in the Soviet Union. Like Stalin and many other dictators, Napoleon justifies this violence by suggesting that it is all for the greater good, but also that the farm is constantly under threat from the outside. The humans, Napoleon claims, are conniving with Snowball to destroy the animals' ideal society. If the farm is always in crisis, then Napoleon can always justify extreme means to supposedly protect it.