Before Chapter 5, Napoleon worked mostly in private, convincing the other animals that he was a superior leader and building a power base. When he uses his vicious dog army to expel Snowball, he changes from a co-equal leader under Animalism to a dictator, an ultimate ruler of the farm:
In future all questions relating to the working of the farm would be settled by a special committee of pigs, presided over by himself. These would meet in private and afterwards communicate their decisions to the others.
(Orwell, Animal Farm, msxnet.org)
By relegating all high-level decisions to himself and the pigs, Napoleon removes the threat of democratic voting and independent thought from the farm, creating instead a fiefdom where he and the pigs live in comfort while their servants -- the other animals -- work hard. His slow evolution from equality to leader is seen both in his use of Squealer to sway public opinion, and in his refusal to actually implement decisions that would help the other animals, preferring to keep them overworked, exhausted, and confused, unable to raise protest against him.