I don't have much of a mean streak, and as a result I find extended bullying and emotional abuse rather bewildering. People put a remarkable amount of work into making each other miserable, and while I don't have a general theory of the motivations, I think I understand a piece of the mechanism.
In the case of personal (rather than institutional) abuse, I think the abuser is triggered  when they see the abusee  being comfortable or happy. 
Depending on the amount and duration of the abuse and the temperament and choices of the abusee, the abusee may internalize the lesson that feeling good leads to being attacked. This means that a feeling of security needs to be built up for recovery to be possible.
One of the things a competent therapist can do is to underline their own happiness when a client is in better emotional shape.
Meditation can lower general background anxiety.
Cognitive psych is a way of fading out the reflexive fear by checking on whether attacks are really likely, how serious they are likely to be, and developing effective ways to handle various situations.
While religion isn't my path, believing that God is on one's side is another way of defusing the feeling that the abuser's emotions are the most important thing.
 I don't think this is a very conscious process, though I think sometimes it takes the form of believing that if low status people are too happy or comfortable, they're getting above their station. Also, every instance of happiness or comfort doesn't have to result in abuse for the process I'm describing to happen-- attacks just have to be frequent enough to produce a background sense of danger.
 I'm not sure why I have a strong preference for 'abusee' over 'victim' or 'survivor'. It may be that I want to handle this as an abstract system, or I may come up with a different plausible theory later.
 Hypothetical motivations: the abuser wants to maintain dominance, possibly mostly for its own sake or possibly to get tangible services cheaply, or perhaps the abuser is unhappy in a way that seeing someone happy makes them feel bad.
Afterthought: There may be a different pattern of an abuser being entirely internally driven to attack, so that the attacks are really unconnected to the abusee's emotional states. I'm saying this because I don't want to overgeneralize from what's going on with me, but I don't know whether recovery from truly random abuse would take a somewhat different path.
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