In chapter 1, Old Major provides the reasons why the animals have to rebel against humans. He states that animals live short, miserable lives filled with drudgery. They are given just enough food to survive and are forced to work to their last days. He mentions that once they are not useful any longer, they are cruelly slaughtered. None of the animals in England are happy, for they are not given a moment's rest and are denied even the right to retire. He asserts that animals have no freedom and that their lives are epitomized by misery and slavery.
In brief, Old Major is stating that the animals are being exploited, abused, and oppressed. They are treated as mere objects.
Further in his speech, Old Major proclaims that the animals' harsh conditions are unnatural, for there is enough food and resources available for all to share equally. He states that all the animals can live in dignity and comfort. The animals have to consider why they have to endure such hardships. Practically all they produce is stolen from them by human beings. He emphasizes that it is Man who is the enemy. Man is the one responsible for their suffering, and if Man should be removed, hunger and drudgery would be gone forever.
All of the above factors are causes for rebellion, and that is exactly what Old Major urges the animals to do. He wants them to stand up against Man's tyranny and rule their own lives. He believes that the animals are more than capable of managing their own affairs and ensuring equality. Although he does not know when the rebellion will happen, he states that the earlier justice is done, the better.
Old Major's words are heeded by all the animals, and they soon secretly start working toward their revolt by educating each other and creating committees. The process is led by the pigs, who are seen as natural leaders since they are the most intelligent of all the animals.
The actual Rebellion is triggered by the humans' neglect on Midsummer's eve—also called the summer solstice (21 June). On this specific occasion, Mr. Jones has gone into Willingdon, where he gets drunk, returns on Sunday, and goes directly to sleep. His men neglect to feed the animals and go out rabbiting. By evening the animals have still not been fed and they are starving. One of the cows breaks down the door of the store-shed with her horns and the starving animals pile in, helping themselves from the bins.
Mr. Jones then wakes up and hears the commotion in the shed. He and his men soon use whips and lash out at the animals, but the hungry creatures are determined and turn against their tormentors. They succeed in driving Mr. Jones and his men off the farm. Mrs. Jones secretly leaves soon after. The animals celebrate their victory and claim the farm, which they later rename "Animal Farm."
It is sadly and tragically ironic that Old Major's ideal is never truly realized because the pigs assume leadership of the farm and, to an ever-growing degree, assert their authority through manipulation, threats, propaganda, and deceit until they have assumed total control. Napoleon becomes their dictatorial leader, and the other animals are subjected to even worse conditions than those they had experienced during Jones's rule.
However, the actual rebellion didn't occur until after Old Major's death when Farmer Jones and his men forgot to feed the animals for a long period of time. Fed up with being hungry and neglected, the animals got Boxer to kick open the feed stores so they could eat. When they figured out they had within them the power to fend for themselves, they drove Farmer Jones, his wife, his workers, and the Raven (church) off, and renamed the farm Animal Farm.
After not being fed for a full day, one of the horses knocked the door of the food shed in and the animals began feasting. Mr Jones saw and him and his men came out with whips and began lashing out at the animals. The animals then fought back.