I think it's likely that the civilizing effect of literature has done most of the work, and still continues to do. Look at Steven Pinker's book, The Better Angels of Our Nature: Why Violence Has Declined. It proves beyond any shadow of doubt that violence has declined dramatically throughout the centuries. There are various reasons for it: the rise of the state, Leviathan, the monopoly of violence, children's rights, animal rights. They're all positive signs.
Martin AmisHe was an artist when he saw society: it never crossed his mind that society had to be like this; had any right, had any business being like this. A car in the street. Why? Why cars? This is what an artist has to be: harassed to the point of insanity or stupefaction by first principles.
Martin Amis