I'm sticking my neck out next to thisis. I'm sorry, Proud, this is a bit of a thread diversion.
I find it impossible not to associate long-term abusive behaviour with personality disorder. The more I learn, the more aware I become that the abusive mindset is strongly dictated by "old brain" instincts; there's a lack of "front-brain" thinking. We're all programmed to feed, fight and fuck - but a million years of evolution has taught us the value of social bonds, give-and-take in the community, and so forth: the sharing & caring moderators.
We socialise children from toddlerhood. In teaching them not to hit and steal, to share and to look after others, we show them what to do with the newer parts of a human brain. We continue, through childhood, to help them evaluate social situations, learn to interact and develop a set of moral values.
In some people this process gets interrupted. Some studies of people with personality disorders have shown abnormalities in the old-brain to new-brain communications. It's unclear whether the abnormalities are genetic or developed. They look similar to anomalies noted in autism-spectrum disorders, although symptoms are different.
I wonder whether there are two distinct, yet connected, sources of such disorders. When incompletely socialised adults bring up their own children they will, inevitably, fail to help them develop the full set of social & moral skills: they can't teach what they don't know, or provide nurturance they don't comprehend. If the brain anomalies are genetic, some children will inherit them. Even if not, the parents' impairments will impair the child's development.
Thinking like this leads me to theorise that some abusers can retrain themselves - they can learn, in later life, to activate the 'social' pathways of their brain - while others may be literally unable to, lacking the mental capacity to do so. There's a problem, of course, in that most abusers would choose not to bother, whether equipped or not, since abusing gets them what they (think they) want.
The term 'Personality Disorder' gives us a very useful shorthand to describe people with rigid, two-dimensional personalities. Since it's also the term used for a set of clinical diagnostic tools, we have to be careful to stress that we're talking about a human phenomenon, not a psychiatric diagnosis. With that in mind, I'm sorry to say I think they're widely prevalent in all our societies; perhaps it's just another expression of patchy evolution. Unlike fully-socialised people, those with disordered personalities follow predictable patterns of behaviour and communication. There are odd-seeming gaps in their comprehension of life.
I agree with Dr Bancroft that it's fairly futile to get them to change. Life's short, and there are socialised folk you could spend your time with instead.
Ramble over 