I would say that Sigmund Freud's definition of hate most accurately explains the motivation for the feud between the Montague and the Capulets. Both sides of the feud believe that each other are the source of their unhappiness. They really have no purpose for believing this other than the fact that their ego forbids them from thinking that the other is equal to themselves. They are both extremely wealthy families, therefore they have quite a big ego, to the point where each one is incapable of accepting the other as an equal entity. It is themselves and their ego that truly causes their unhappiness.
