according to you,who or what is responsible for the chaos in Animal Farm?

First this is an allegory to human fallibility. In particular, Stalinist Russia or other autocratic states that have littered our history. Now the problem in the book becomes certain animal's lust for power and dominance. So, Old Major begins with a dream; a utopian farm for all animals. Napoleon takes the dream and twists it. Like humans certain animals fall into subservience. Power for animals at the top of the chain becomes intoxicating. The animals become just like their human oppressors. The farm ends up gripped in an even worse form of terror. Animals like Napoleon inflict their drive and vengeance on each other.

In my opinion the cause of chaos on the farm was Mr. Jones. If he was not so careless in the up keep of his farm then the animals would have not been so poorly treated. They eould have enjoyed being on the farm because they were well looked after. Old major would have no reason to put the idea of a rebellion into the minds of the animals.