In "Animal Farm," who is the animals' enemy?

The animals' have more than one enemy, though some aren't revealed until later in the story. Their most obvious enemy is 'Man', due to the abuse suffered. This hatred of man and fear of Jones is what keeps them from seeing who their real enemies are. Later on, its apparant that their real enemies were among them all along, perverted by their luxuries and thirst for power. Napoleon and Squealer, as well as the dogs, have become their enemy, and have taken on the same role that Jones had before he was ousted. They've even started an institution of tyranny through newly arriving pigs.  You also have Pilkington & Fredericks, two farmers who try to find ways to use and trick the animals through trading with them, only to have Fredericks open attack them. One could also say that their most dangerous enemies are themselves; for whenever they notice something is wrong or unjust, its always that interior argument 'Napoleon is always right' which keeps them from doing anything about it.