One rhetorical technique Old Major uses is vilification; by placing all of the world's woes on the shoulders of humans, he divides the world into two camps: "us," and "them."
"Is it not crystal clear, then, comrades, that all the evils of this life of ours spring from the tyranny of human beings? Only get rid of Man, and the produce of our labour would be our own."
(Orwell, Animal Farm, george-orwell.org)
He allows no room for argument, since it is obvious from his speech that humans are slave-masters instead of keepers. If someone disagrees with his sentiment, they are "human-sympathizers" and therefore on par with the enemy. By vilifying specifically instead of broadly, he sets up all humans to be the enemy of animals. This tactic is exemplified in the works of Saul Alinsky, who wrote: "One acts decisively only in the conviction that all the angels are on one side and all the devils on the other" (Alinsky, Rules for Radicals).