I've encountered some interesting considerations about inequality in my wandering readings. In sum, it's a growing problem. Of course, some inequality is inherent in humans, as in other primates. But what I'm referring to is a pervasive inequality that becomes dysfunctional, not to mention unjust.
A good staring point is this Five Books interview with Darin Acemoglu. I think that this shows, like most social phenomena, there is no one answer to the emergence of a phenomenon. See also this presentation by him.
Jack Goldstone, another important social scientist, weighs in with this blog post.
Finally, welcoming back the truth-teller of Iowa (even if he no longer works here), Donald Kaul. Kaul is correct: don't say fault for the precarious situation is evenly divided between Republicans and Democrats, because it isn't. We'll be damned lucky if we don't repeat the 1930's that way we've set things up like the 1920's.