There is a lot of it about. I sometimes take the long view to try to understand it.
Until 1994, the right for a husband to abuse his wife was written into the marriage contract in the UK, as there was no such crime as marital rape. Essentially a wife had signed away her right to bodily autonomy if her husband wanted "sex", because that was his right.
Financial abuse has only recently become a crime - before then it could have been defended as just a part of traditional marriage. A few decades before that, financial control was enshrined in law, as a woman needed her husband's agreement to get financial products like a mortgage.
Police never used to take domestic violence seriously in the slightest, it was seen as a private matter. I think this has finally changed somewhat.
Violence against children was normal and even encouraged at school until the 80s (90s for private schools). Many adults around now were beaten as children, and told it was normal and for their own good.
We've only very recently developed a common language to describe emotional abuse and abusive dynamics.
So, thankfully things have improved somewhat in the past few decades, but for many centuries previous, relationship abuse was considered normal and even a positive thing.
There are some interesting writings about "breaking the cycle" from Jung and others who follow his path. The idea being that abuse has been passed down from generation to generation for so long, that we need to actively work towards breaking that cycle of abuse to ensure future personal and societal happiness.