This is Paul Krugman's chart of the year, and it's easy to see why

[NACBA]

If you follow economic news, the chart shouldn't be all that surprising. India and China grew dramatically between 1988 and 2008, as did a number of smaller middle-income nations, accounting for the big spike in incomes for the global middle class. Meanwhile, top incomes in developed countries surged while median incomes stagnated, forming that Krugman calls the "valley of despond."

http://www.vox.com/2015/1/4/7482385/krugman-chart-valley-despond