In Animal Farm, Napoleon most fears an educated populace. He works hard to keep the other animals "in the dark" about what's really transpiring on the farm and his true intentions. Additionally, he keeps the other animals in fear and beholden to his leadership. He convinces them, through his "minister of propaganda" (Squealer), that they need him in order for their survival. To accomplish these ends, he first enslaves thier minds which insures their overall enslavement.
Napoleon thinks that Snowball is the only other animal on the farm that could rival his desire to control others. Because of this, he creates a situation whereby Snowball is scapegoated and run off the farm. This clears the path for him to take control of things.