how is the windmill destroyed? why does napoleon blame snowball?

By autumn, the windmill is half finished. One night in November, violent winds ravage the farm and destroy the windmill. Napoleon quickly blames the destruction on Snowball. This gives Napoleon an excuse to get rid of his rival. He sentences Snowball to death and offers half a bushel of apples and the title of “Animal Hero, Second Class” to any animal that detains him.