In Animal Farm, Chapter 5, what is the power struggle between Napoleon and Snowball?

Napoleon and Snowball begin to disagree on every issue: 

These two disagreed at every point where disagreement was possible. If one of them suggested sowing a bigger acreage with barley, the other was certain to demand a bigger acreage of oats, and if one of them said that such and such a field was just right for cabbages, the other would declare that it was useless for anything except roots. Each had his own following, and there were some violent debates. 

Snowball spends large amounts of time designing the plans for the windmill. He wants the animals to start building upon completion of the plans. Napoleon would rather spend their efforts on food production. 

Snowball wants to incite rebellion in other farms but Napoleon wants to focus on the defense of their own farm. Napoleon simply disagrees with Snowball no matter what the issue is. Napoleon has no intention of working with Snowball or of considering any of his ideas. 

The day comes when the animals are to vote on whether or not to start building the windmill. The rivalry between Napoleon and Snowball comes to a climax here. When it seems that the animals are going to side with Snowball, Napoleon sabotages the vote and has Snowball chased off of the farm. Napoleon (and Squealer) downplay Snowball's role in the Battle of the Cowshed and Napoleon says the windmill will be built and that he'd never opposed the idea. Napoleon will continue to rewrite history and the commandments to suit his increasing greed for power.