how does ignorance lead to the social and political oppression in animal farm

When one is ignorant one does not typically think for himself or herself. The animals, except for the pigs, were unable to read and write (or only minimally) and thus had to believe what the pigs told them. They were oppressed because they were unable to have any opinion and so they blindly followed what the pigs told them. They could not see any way to break free.