Why is violence against women often carried out by those closest to them?

Three recently released studies, featured in the Lancet, Science and released through WHO, paint a chilling picture of violence against women.

One study found that over a third of all homicides of women are committed by a current or former partner, while the other two showed that almost every third woman experienced violence at some point in their lives, either physical or sexual, at the hands of a partner.  

Although Europe, as can be seen in the figures above, is somewhat below the world average, the figures remain worryingly high.

What do you think can be done to lower these numbers? And what are the reasons that they are so high?