Before the revolt against Farmer Jones, the animals, inspired by the vision of Old Major, dreamed of an existence that was dominated by equality and justice, fairness and freedom from the control of humans.
After the revolt, Snowball becomes very active in organizing committees and researching ways to improve the efficiency of the farm, he tries to carry out the vision of Old Major by improving the output of the farm for the benefit of all animals. As Snowball's popularity starts to rise, Napoleon, who says very little in public, begins to recognize that Snowball is a threat to his desire to hold total power and control over the newly named Animal Farm.
In a power grab, fueled by his jealousy of Snowball and his need to be the supreme leader, he has his dogs run Snowball off the farm. Napoleon's selfishness is at the heart of his desire to control the farm, he has no interest in improving the farm or making life easier for the animals. In fact, he doesn't care how hard they have to work as long as he can get rich from the output of Animal Farm.
In an effort to establish an atmosphere of fear on the farm, Napoleon starts to execute animals randomly when they are accused of actions that are deemed against the supreme leader. Chickens are executed for their attempted revolt at having to produce eggs for sale, porkers are slaughtered for having contact with Snowball. Anyone who opposes Napoleon or complains about the lack of food or the hard work is subject to execution.
Boxer, the cart horse who works so hard on the farm and runs himself into the ground, he actually gets sent to the slaughterhouse instead of the ideal of living out a retirement in the grassy knoll, waiting for a natural death.