Zackaria actually covers that in the book as well. In (very) short, as the rest rise up, they experience a great deal of social and economic changes. These changes increase the quality of life, and helps balance the trade imbalances naturally... which in turn slows down the rate of increase. This is shown specifically in China today, as it was previously in Hong Kong, Taiwan, Korea, and Japan. They don't crash to where they once were, but the market forces then turn to investment in new territories but only after the amount of economic growth becomes sustainable on some level on the countries that it was previously at.
Get the book... best non-fiction book I've read in 20 years.