Because Napoleon is supposed to represent Stalin (which is slightly ironic considering the fact that Napoleon's invasion of Russia was another of the causes that drove Soviet thinking and policy) his method of taking power in some ways mimics that of Stalin's. He makes a deal with anyone he needs to and even starts using animals against other animals in the case of the puppies. In this way he mimics much of what Stalin did, making deals with enemies and then working behind their backs, all to consolidate his power over the people. He also ruthlessly eliminates anyone opposed to him just as Stalin did through the pogroms against any people who were allied to the old powers or weren't blindly loyal to him.
napoleon got controll by forcing snowball out. this says, he's a ruthless, competitive ruler, who will whipe out his opponents and sell his friends for a penny.
Napoleon fought along with Snowball to free the farm from human control. Then he attacked Snowball to seize control of the farm and to direct all its activities, similar to Leon Trotsky and Joseph Stalin who struggled over the control of Russia. Trotsky supported Permanent Revolution (just as Snowball advocated overthrowing other farm owners), versus Stalin who supported Socialism in one country (similar to Napoleon's idea of teaching the animals to use firearms). Napoleon, while promising power for the people er.. animals, always had designs for power.