What was the issue that the animals had to decide between when it came time to vote to have a windmill or not?
I think that the fundamental issue that the animals had to decide between in terms of the windmill was which vision of the farm was to be embraced. Chapter five depicts the growing division between Snowball and Napoleon. Disagreeing at nearly every turn, both pigs feature incompatible visions of the farm. Both pigs are seeking to win over the other animals, and this becomes the central issue that needs to be decided by the animals. The windmill becomes the epitome of this disagreement. Snowball presents a futuristic vision of the farm in which the animals are literally owning the benefits of the means of production. The vision of the farm under windmill supplied power is the realization of Animalism. Napoleon dismisses it as nonsense, even urinating on the schematics. The debate between both pigs take center stage. Both pigs give their speeches in the attempt to convince the other animals. Napoleon realizes how convincing his adversary is as the animals are able to accept his vision. It is for this reason that he has the dogs run Snowball off the farm. For the animals, the fundamental issue is which vision of leadership is going to be accepted. Napoleon's "top down" and centralized notion of authority is pitted against a more collective and empowering vision of Snowball. When it comes time to vote for a windmill, the decision has become a referendum on one of the pigs. Napoleon realizes this and sends the dogs to chase Snowball off the farm, thereby centralizing his power and solidifying his control of the farm.