What happened to the windmill in chapter six of Animal Farm? What caused it to happen?
The windmill is intended by Napoleon to stand as a symbol of the victory of Animalism, of the common endeavor of the animals coming together to build an enduring monument to Napoleon's genius. In reality, it comes to epitomize how badly things are being run at Animal Farm. The windmill is a jerry-built vanity project, a rickety structure not built to last. It stands as a symbol for Napoleon's rule, but not in the way he intended it. Like everything else to do with Napoleon's dictatorship, the windmill is all just for show, something that he could point to as tangible evidence of the success of his regime.
But when it collapses due to a gust of wind, his credibility has been damaged. So he has to make a scapegoat of Snowball once more. He is the bogeyman figure whose blackened name can be invoked any time something goes wrong. To Napoleon, the collapse of the windmill hasn't been caused by the forces of nature; it is a deliberate act of sabotage by the forces of darkness: Snowball. In order to maintain his iron grip on power, Napoleon must always be seen to be right. If something goes wrong, it will never be his fault, never his responsibility.
In November, a harsh southwest wind comes and knocks down the windmill that the animals have labored so long to build. It is in ruins. Napoleon, however, blames this destruction on Snowball, saying he came to the farm under cover of darkness to destroy the windmill. He even shows them pig footprints that seemingly lead to a hole in the hedge. The other animals are deeply shocked at Snowball's treachery. Humans on the other farms, however, maintain that the windmill's walls were thin, causing it to be too weak to withstand the high winds. While the animals insist this was not the case, they still decide to rebuild the windmill with walls twice as thick, three feet rather than just eighteen inches.
The windmill, which has not been built very well, is knocked down by a violent storm. Since Napoleon took credit for the windmill plans, it would be logical to blame Napoleon for its destruction. However, Napoleon avoids this by blaming the destruction on the deliberate attack of Snowball. Napoleon makes Snowball a scapegoat, and uses the incident to make Snowball the official enemy of all the animals. He even plants pig tracks near the windmill, and claims that they are certainly Snowball's. "Whenever anything went wrong it became usual to attribute it to Snowball."