What turns the battle of the windmill in the animal's favor?

Being frightened by Fredrick and his men they ran into the barn and watched as the men tried to destroy the windmill. Napoleon questioned why they would try since the walls were too thick, but Benjamin understood that they were building a hole to shoove some dynamite to explode the windmill. when it bursted into flames as if it was never there the animals in such rage, savagely attacked the men as they tried to flee making the battle of success.

in other Words, the distruction of the windmill gave the animals favor realizing their hard work went to waste.