In chapter 2, the animals successfully throw Mr. Jones off his own farm because of his lack of leadership, care, and management of them and the farm. By chapter 3, the animals have taken over full control of the farm, renamed it Animal Farm, and are doing a rather good job maintaining and managing it. The rebellion and overthrow of Mr. Jones happens at Midsummer, and Farmers Frederick and Pilkington worry about what is going on at Animal Farm. As a result, Pilkington of Foxwood offers some of his men to help Jones take back his farm; but an attack doesn't happen until October, a few months later. Unfortunately, Mr. Jones mobilizes too late, because Snowball stands ready with strategic defensive actions.
"They were gored, kicked, bitten, trampled on. There was not an animal on the farm that did not take vengeance on them after his own fashion. . . . At a moment when the opening was clear, the men were glad enough to rush out of the yard and make a bolt for the main road. And so within five minutes of their invasion they were in ignominious retreat by the same way as they had come" (38).
The above counter-attack happens as animals who were hidden from view at the beginning of the battle suddenly emerge from the cowshed and win the day due to this strategic ambush. Had Jones attacked more quickly after being overthrown, he may have had a better chance to reclaim his farm. On the other hand, if Jones had not been too drunk to feed the animals and maintain his farm, he may not have lost it in the first place. Therefore, the cause of the Battle of the Cowshed is the result of Mr. Jones's lack of preparation, leadership, and management of his farm in the first place, and a slow response to taking back his farm in the second.
The cause of The Battle of Cowshed is the retaliation of Mr. Jones after the rebellion. The animals have already overthrown Jones and some amount of time has passed. Jones comes back with a small army of men presumably to beat the animals back into submission and to regain control of his farm. Despite Jones advantages, including weapons such as a firearm, the humans are defeated after Snowball employs some military tactics learned from Julius Caesar. The animals are victorious although they do endure some casualties and adopt some of their first human behaviors by commemorating the battle annually and bestowing medals.