Answer:
Napoleon wants to undermine Snowball and maintain control of the farm.
Step-by-step explanation:
George Orwell's allegorical novella "Animal Farm" tells the story of how a group of farm animals rebelled against the human masters and then again fought for power among themselves. In their attempts to create a society for themselves by themselves only led to their downfall and return back to the 'true' form of government- that is among the humans.
The rebellion against the humans was a success in the beginning. Old Major, an award winning boar and the 'unofficial' master of the whole farm had delivered his "dream" where the animals are free of the humans and living a life free of oppression and control. But after his death, three younger pigs Napoleon, Snowball and Squealer decided to make the pigs as the authority over the other animals in the farm. But even this order doesn't last long. Napoleon rebelled against Snowball, in a bid to gain the maximum authority. The excerpt given in the question is from Chapter 6 of the text where Napoleon had accused Snowball of attacking the farm and destroying the windmill. His motivation for blaming Snowball for the destroyed windmill is because he wanted to undermine Snowball and maintain control over the farm.