What signs of unstable conditions indicate that the Manor Farm was fertile for a rebellion?

Animal Farm is an allegory which means that it can be read on two different levels. Each character or event in an allegory stands for something else. Orwell's purpose then was not just a simple fable of animals on a farm but also a critique of the Russian Revolution. At the beginning of the novel the conditions on Manor Farm allegorically mirror the conditions of pre-revolutionary Russia. For example, Farmer Jones could be compared to the Russian Czar in his negligence of his nation's problems. The farmer is depicted as drunk and irresponsible. He basically only gives his animals enough food to keep them barely going. Old Major describes their plight:

"We are born, we are given just so much food as will keep breath in our bodies, and those of us who are capable of it are forced to work to the last atom of our strength; and the very instant our usefulness has come to an end we are slaughtered with hideous cruelty...The life of an animal is misery and slavery: that is the plain truth."

If the farmer is Czar Nicholas then Old Major is most likely either Marx or Lenin, the men who formulated the philosophy behind the revolution. Old Major describes dire conditions where animals are treated poorly and even slaughtered when they are no longer useful. In Russia, the serfs, or peasants, who worked the farms were often unable to produce enough food for Russia and just before the revolution there were major food shortages across the country.
Moreover, Russia was engaged in World War I and tens of thousands of Russian men were slaughtered on the eastern front, most lacking requisite supplies and some even without guns. Old Major also speaks of the fact that the animals do all of the labor and produce all of the goods which the farm sells. In contrast, Farmer Jones produces nothing and does little work. Likewise, the Russian aristocracy, many centuries old, produced little yet reaped the benefits of Russia's production.
Finally, one important condition of rebellion was that the animals had leaders who were willing to discuss such a revolution, especially Old Major who places the seed of rebellion in the minds of the animals. The revolution ultimately takes place spontaneously but is certainly prompted not only by the unsatisfactory conditions on the farm but also by Old Major's speech suggesting the idea that the animals would be better off without Farmer Jones.