Income inequality is an increasingly difficult problem to pin down, but it appears it is not what it seems. See Paul Krugman’s review of Saving Capitalism: For the Many, Not the Few by Robert B. Reich.
Something else began happening after 2000: labor in general began losing ground relative to capital. After decades of stability, the share of national income going to employee compensation began dropping fairly fast. One could try to explain this, too, with technology—maybe robots were displacing all workers, not just the less educated. But this story ran into multiple problems. For one thing, if we were experiencing a robot-driven technological revolution, why did productivity growth seem to be slowing, not accelerating? For another, if it was getting easier to replace workers with machines, we should have seen a rise in business investment as corporations raced to take advantage of the new opportunities; we didn’t, and in fact corporations have increasingly been parking their profits in banks or using them to buy back stocks.