Last week, economist Greg Mankiw posted an interesting chart (which he got from Paul Krugman) about the trend in the reported income of the top 1 percent of earners in the United Kingdom:
The broad pattern is very similar to what U.S. data shows. The figure suggests that the explanation of growing inequality over the past several decades cannot be U.S.-specific but must have broader applicability.
You can generate more plots like this here. You find a similar U-shaped pattern in Australia, Canada, Ireland, and New Zealand but much less so in France, Germany, Japan, and Sweden.
I also found this video about income inequality by Prof. Steve Horwitz informative.