I think that part of Orwell's genius is that he is able to show how theoretical ideas become corrupted in political reality rooted in pragmatism. There is a definite difference between seeking change and then holding political power. Orwell shows that political theory and political reality are two different beings in how Old Major's idea of Animalism is reflected on the farm.
Animalism was the spirit used to foster and facilitate the revolution. Once the other animals did the difficult job of removing Jones and the other humans from the farm, it became clear that the political reality governing the farm was used Animalism as a justifying theory. However, Orwell shows that its use was only theoretical. The leadership of the pigs and the coveting of power seen in Squealer and Napoleon led to the use of the theory in name only. The notions of "Animalism" did not compel Napoleon to surrender power. This is where his conflict with Snowball becomes its greatest. Orwell shows that in the course of political power, the need to exert and demonstrate control trumps all theoretical notions. As this tension develops more, Animalism becomes diluted. The ideas of collective power, shared decision making, and equality in control are substituted for consolidation and decision making at the highest of levels. By the end of the novel, Animalism has disappeared with there being no difference between the pigs and the humans. It is in this statement in which Orwell makes clear that modern political reality is one where there is only power and theory is only as good as substantiating the existence of control in modern government.