For decades, America’s economic might legitimised the dollar’s claims to reign supreme. But, as our special report this week explains, a faultline has opened between America’s economic clout and its financial muscle. The United States accounts for 23% of global GDP and 12% of merchandise trade. Yet about 60% of the world’s output, and a similar share of the planet’s people, lie within a de facto dollar zone, in which currencies are pegged to the dollar or move in some sympathy with it. American firms’ share of the stock of international corporate investment has fallen from 39% in 1999 to 24% today. But Wall Street sets the rhythm of markets globally more than it ever did. American fund managers run 55% of the world’s assets under management, up from 44% a decade ago.