Still, there is debate about the sustainability of China's economic growth and its capacity for global leadership, David Kelly, a director of research at the Beijing-based advisory firm China Policy, observes. "If you speed up very fast," Kelly says, "you find that you're up against a barrier of other powers bandwagoning against you" — resulting in diplomatic isolation. "The sustainability of wealth and power is very much up for debate," he says. Assumptions about China's future economic strength rest on the country's past success in meeting U.S. and European manufacturing needs of the 1990s and 2000s. In other words, "That growth was based on the world economy at that time," he says, "and it's no longer the same world economy."