I think that Orwell makes the argument that Napoleon succeeds in asserting control because he was concerned with both the revolution and his position after it. Part of what makes Napoleon so successful as a leader is that Orwell constructs him as a leader who has one eye on the present and another on the future. For example, in chapter 3, Snowball exerts his energy organizing the animals into committees, while Napoleon takes the nine pups for his own. They will later become his guards and his own "police force" that will instill law and order when times are difficult. This is most notably seen in chapter 7 and the forced confessions moment. The fact that Napoleon is operating in a position to consolidate his own power both in concert with and divergent from the revolution is what makes him so successful in maintaining and increasing his power over Animal Farm. It is in this light that Napoleon is seen in both his most cunning and most brutal form as a leader.