...What Mr. Milanovic shows is that income growth since the fall of the Berlin Wall has been a “twin peaks” story. Incomes have, of course, soared at the top, as the world’s elite becomes ever richer. But there have also been huge gains for what we might call the global middle — largely consisting of the rising middle classes of China and India.
And let’s be clear: Income growth in emerging nations has produced huge gains in human welfare, lifting hundreds of millions of people out of desperate poverty and giving them a chance for a better life.
Now for the bad news: Between these twin peaks — the ever-richer global elite and the rising Chinese middle class — lies what we might call the valley of despond: Incomes have grown slowly, if at all, for people around the 20th percentile of the world income distribution. Who are these people? Basically, the advanced-country working classes....