The Battle of the Windmill is a stylised representation of World War II.
Fredrick's men approach and blow up the windmill. The animals are incensed and immediately retaliate.
The fighting is violent and bloody: Racer uses his hooves to 'smash heads in'. And while the animals ultimately 'win', they are exhausted, weary, and have lost many of their members. In fact 'nearly everyone was wounded'.
Immediately, Squealer declares that the Battle was a stunning victory for Napoleon. However, the other animals are not so sure. The heavy losses and suffering are still fresh in their minds. Squealer then proclaims that it must be a victory as the animals have regained the farm. This, again, does not convince the animals. Boxer epitomises this when he states, "we have won back what we had before". That is, no change (for the better) has been secured, but sacrifices have been made.