How does this quote illustrate the major concerns of George Orwell's novel Animal Farm?
Twelve voices were shouting in anger, and they were all alike. No question, now, what had happened to the faces of the pigs. The creatures outside looked from pig to man, and from man to pig, and from pig to man again; but already it was impossible to say which was which.
Animal Farm is an allegory for the Russian Revolution. More generally, it is an allegory of the dangerous route a rebellion can take. Initially, the animals rebelled against Mr. Jones (man) because they wanted a better life and they wanted to share in the rewards of their work, rather than it all go to Mr. Jones. In its inception, the rebellion was founded upon logical, sensible motivations.
Over time, Napoleon and the other pigs (excluding Snowball) increased their power and made the other animals work harder. The pigs had become as oppressive as man, Mr. Jones, had been in the first place. The pigs and men, both of whom let power corrupt their leadership, became indistinguishable from each other. The main concern here is that a rebellion is pointless if it results in the same oppressive state (or worse) from which it had tried to rebel. As we see at the end, the so called rebel leaders (pigs) actually become friends with their former oppressors. That is, until both sides accused each other of cheating. Here the similarities between pigs and men continue with dishonesty and mistrust.