Perhaps too off topic, but I’ve often wondered how the descendants of Vikings, once considered the most terrifying raiders of the sea, are now some of the most egalitarian and nonviolent nation states.
I'm no historian, but my best guess it that it's just correlation and that the main underlying cause of "civility" is wealth. When your citizens are struggling to survive, they (at least in their own minds) don't have time to think about women's rights, racial prejudice, etc. The progressive countries of the world just happen to be a few decades ahead on the technology timeline. There are obviously other factors, but I think that's the big one.
Wealth is probably the immediate cause, but in time, it seeps into the mentality of a people. The result is a society where trust in other people is low, everyone treats everyone else like they are out to cheat you, have little civic spirit and don't want to spend energy for the betterment of the whole. They would vote with whomever gives them bigger short term gains, damn with the future and consequences, other people will inherit them. It's hard to turn a mentality around, you just have to wait for older people to die and be replaced.
An interesting side note on this, the descendants of the Vikings were also the Norman's, that later invaded England, and even sailed around to Southern Italy and conquered a place down there as well (I think it was somewhere roundabout Sicily?). They developed the state of the art castle building techniques, sailing techniques, extensive trade networks, and even some interesting governing techniques (women had land-owning rights) that enabled them to conquer and hold much of Europe over time. It might be that they were "the most terrifying raiders of the sea" because they had cultural values that prized technological advancement and decently good governance, and then spread out to nicer climates (good motivation to try something new...). Interaction and adoption of values from other cultures probably helped bring down the violence after a certain point. And like someone else pointed out, when you get wealthy and own the kingdom, you typically want to develop a culture of preservation rather than raiding.